I post this in the spirit of trying to help via my experience, not as contradictory. Roy, you should know I think the world of you.
This new(er) chassis is a nice alternative to the solid aluminum ones. Of course you know I prefer wood. The good news is heatsinks can in fact be mounted on the bottom side of the board. I'll post this again for reference:http://www.flickr.com/photos/59541088@N08/8606072618/in/photostream
I use cut-off pieces of plastic wire ties underneath each heat sink as "spacers" when soldering them to the board. This raises the heatsink off the board about 1/8 of an inch, eliminating the chance of them coming into contact with a ground plane or other traces, and it also provides a bit more air circulation for coolong. Remove plastic pieces when done soldering.
The only other thing one has to do is make sure the 1084/1085 Volt Reg. IC is properly oriented as it will now be mounted on the opposite side of the heatsink it would normally be mounted on. Although now offset, the pins are long enoungh to bend back under the heatsink and into the holes on the board, bringing them back into proper orientation.
Done this twice now with no heat issues or any long term detremental effects noted. My cases are well ventilated though. The only thing I have mounted on the PCB's top side are the jumper wires and the tube sockets. For spacers between the board and chassis I use grommets. They provide both the offset and vibration dampening. A drop of crazy glue keeps them in place.
If you countersink 3/4 inch holes on the front panel about 5/16" deep (I use fostner bits as they cut flush) you could easily move the controls from the top to the front. Of course the controls must have shafts long enough to go through 1/2" of wood and still have enough length to mount a knob on. Not a problem with elma (goldpoint) switches.