The back of the case. The protruding aluminum part below the power supply (which would not fit inside due to the presence of a middle shelf thing, now the motherboard shelf), is a frame that once held a pair of 120mm Muffin fans. Since I'm not going to be putting 45 vacuum tubes back into it... the cooling requirements are far less strenuous. The old fan frame now flips up on hinges to reveal the ATX back panel and slots, and a gap cut in its bottom allows cables to go through.(VXO (vxo))