Hi reglys,
The chassis plate dimensions are given as 10" x 6" on the Crack product description web page (see 'In Depth'). I didn't see a thickness specified; I think it is around 0.080"-0.10" thick. I didn't see base dimensions, though someone else may post them. The material from which the bases are made is roughly 1" x 4" lumber size, which is about 3/4" thick by 3.5" width. The top plate rests in a rabbet cut into the upper inner edges of the pieces of the base; the cut is about 1/8" by 1/8"; again, someone else may post specifics.
I think the width and length of the base are somewhat arbitrary, so long as the top plate is supported and the inside surfaces of the base don't intrude on under-chassis components. Whether height is critical or not is arguable, I've seen posts about some Bottlehead products indicating the height affects airflow and cooling of components. However, if you choose to mod your crack, as many do, the standard height is helpful to accommodate a power supply choke or larger capacitors.
