The wood enclosure that I built for my Crack is shorter than stock, enough so that the Speedball heat sinks stick down far enough to not allow the top plate to rest flat. Would it be okay to attach the TIP-50 transistors to the aluminum top plate itself and then run a bolt through the top plate and into a heat sink like the one I've attached (using some thermal adhesive for better heat transfer)? I'd then run short leads from the transistors to the PCBs with heat shrink over the pins to prevent shorts. The heat sinks would be positioned on either side of the ventilation slots. I thought it might be an interesting visual addition as well. The data sheet for the heat sink indicates 72 degrees C at 4 watts.
Potential Heat Sink:
http://www.digikey.com/product-detail/en/695-1B/345-1095-ND/655563
Potential Heat Sink:
http://www.digikey.com/product-detail/en/695-1B/345-1095-ND/655563