Lots of component legs poking through a mockup piece of cardboard.

I drew the layout by hand on paper, then took it into Photoshop for some cleanup.
Conveniently there are a million different printers at work -- after printing a couple tests, it turned out that the color laser printer put down the waxiest looking ink, which I (scientifically) decided was best. I printed the final mask onto some transparency sheets, and got ironing. Preparing the copper-coated board involved sanding with really fine paper (wet sanding 400 grit or something, it was all I had), then cleaning with isopropyl alcohol until it was free of dust and hand oil.

Here's the board almost entirely stuffed. All the components are standard from DigiKey (which the exception of the 220uf caps, which I got from digging through the billions of caps at Halted surplus. I'm probably violating some audio rules by having long wires going to my transistors, but I wanted flexibility in how I laid out my heatsinks. The cost of new giant heatsinks was a little frightening, but I found these interesting ones at, again, Halted. $7.50 a pop, for a big chunk of aluminum. With one IRFP044 per heatsink, two of the sinks got too hot to touch after 5 mins. I don't think things would get hot enough to damage the transistors, but people would think I did something wrong if the amps were burning hot. So, I might take out R1, and run the amps at 1.66 amp bias. We'll see how that works.

Chassis is standard 17"x10"x3" Hammond Aluminum. I was a little disappointed with how flimsy the chassis felt when it arrived, so I tossed in some aluminum L-channel, which stiffened things up, especially around the heavy toroid. Another weird thing about the chassis is that the cover (aluminum plate) is 1) rounded at the corners and 2) has 4 mounting holes in arbitrary positions. Also, it's a tiny bit bigger than the footprint of the chassis, so the edges hang over a bit. Next time I think I'd just find a place to cut me some aluminum sheet, and skip the Hammond cover. But, after drilling and priming and painting with black semi-gloss, the thing looks much cooler, so I'm pleased overall. I must have scratched the lip edge of the chassis after painting, cause there's a little bare aluminum showing through, which makes me nervous that the thing will be scratch-prone. We'll see. The spraypaint finish looks nice, but I worry that it will chip or be hard to clean up. But, it's spraypaint for now, until I get rich and anodize everything, or risk electrocuting myself with a car battery charger and a garbage can full of anodizing solution.
I put a sheet of paper over the face-down transparency, which was taped around the edges to the copper, so that it wouldn't move around if things got slippery. Fortunately, they didn't - a couple seconds of ironing the paper-covered transparency firmly fixed it to the board. I tried things a couple times on scratch boards, and in the end, it took about 5 mins of ironing for the toner to transfer well. Any little spec on the board resulted in a blob of toner, around which was bare copper; there were a couple places in the final transfer that had little holes. You can see the straight transfer below on the left; on the right is the mask after cleanup with a Sharpie.
Here's the result of the etch -- 30 mins in Ferric Chloride. I used a whole bottle (16oz.) of Radio Shack etchant. The etchant was in a little tupperware container, which I floated in a big tub of a hot water. The whole thing stayed pretty hot, even after 30 mins outside on the porch at night. (The ferric chloride wasn't too bad -- my finger got a little stained once, and it wasn't too pleasant if you stuck your head over the steamy etchant bath, but all in all it wasn't that terrible). I rinsed off the etched boards in the hot water, then used Acetone (available in the paint section of Home Depot) to clean the toner off the copper. Oddly, one board got all smudgy with toner, and the other board was totally clean -- I think this had to do with how much Acetone I used to get off the toner. Doing it again, I'd be more generous with the acetone, possibly even soaking the boards.
But, I'm pretty pleased at how sharp the etch came out -- all my pre-drilled holes ended up in just the right places. Granted, it's a pretty simple layout, and there are no fine traces. Nevertheless I was pleased. (Ignoring the fact that my signature on the board came out backwards :) )
Speaking of chassis drilling, after putting this thing together, I can imagine why so many people love those conical stepped drillbits, the kind that can drill holes 1/4" to 1" in diameter. I only have a small set of bits, and I've been trying not to buy a new tool for every part of this project, but I think $30 would have been well spent for a bit like that. I'd imagine the conical shape makes it super rigid.
Another tool I didn't buy for this project was a drill press. The whole chassis was drilled with a cordless 3/8" drill, and only a couple times did the bit seize up on the aluminum and threaten to rip my hand off. I did borrow some time on a press to drill the pcb. That was sort of interesting. I bought 2 of the tiniest bits at the hardware store (not Home Depot, they didn't have tiny bits), and 3 holes into the board, the first bit snapped. This is with ~100 holes left. But, going on I was super careful to keep the bit exactly vertical (no bending), and I drilled the rest with no breakage. I could tell towards the end that the bit was _significantly_ duller. By the end I was really cranking down on the drill handle, and I think it was by virtue of friction alone that the last holes were made.
Something I haven't totally figured out is how to be really precise with drilling. I measured things twice, made impromptu center-punches with a pushpin or screw, but most of my holes ended up (slightly) off the mark. Everything fits together fine, and it's possible that I'm just being nuts, but I feel like I have a long way to go before I can just measure out holes on two separate pieces of aluminum, drill them, and have them both line up. With the heatsink mounting rails I cheated a bit and drilled through chassis plate and aluminum rail at the same time.

I didn't have any clamps that could reach into the chassis box, and, sadly, I have zero wood scrap lying around, but I do have enough old-medicine-bottle-scrap.

And, behold: The wide-mouth vice-grip. When I first saw this thing, I thought it was sort of silly. This isn't the vice-grip of choice for grabbing onto stripped screws or the like. It is, rather, a cast-metal thumb and forefinger. Any squeezing your thumb and forefinger can do, this tool can do better (and safer!). Here's my no-drill-press drilling setup (Thanks DigiKey!).