So 70% of the heat generated in the 70 cm receiver must be conducted to the case. Heat can be conducted from exposed pads on the bottom of the IC packages to one or two ground planes and then through aluminum standoffs to the case, so this seems possible. Modules like the ACP will be much harder as 90% of the heat must be conducted away and many IC packages will be designed for convection cooling using heat sinks mounted to the top surface.
For Rudak on AO-40 we designed it so the high heat parts were on the top PCB, and then machined a custom module cover so that it was in contact with the IC pakages. Gap filler was then applied and the assembly screwed together.
For the RAM moduls, which mounted at right angels to the main PC board, we ran an aluminum strip heat sink across the module, also in contact with the memory ICs and with gap filler, and then attached to the sides of the module.
Lots of conductive paths!
73,
Lyle KK7P