I did this.
Here are a few recommendations, though:
Extra cooling: Buy heatsink glue (arctic alumina GLUE) and glue a decent heatsink on the pm2 chip of the BV-PPC, and preferably any other IC's (PC gfx-card and DIMM RAM heatsink kits are nice here) and stick a small fan in the case above the BV-PPC, blowing air on it.
Also, stick some low-profile heatsink+fans on both the CPUs, there are 8mm ones available. Cut nice holes in the trapdoor cover for the heatsinks, and put it back on, as it provides support for the BlizzPPC. You may need to heighten the A1200s feet 2-3 mm to allow enough air under the case.
Harddrive: If IDE, use a 2.5" Harddrive. If SCSI, leave the Harddrive outside in a SCSI-tower, where you can also stick your CD-ROM drive and PSU.
Power: Add a custom connector (3-pin XLR is what I used) for +5v and +12v somehow on your A1200, and feed the floppy power port and the BlizzPPC with extra power.
It works, but it's very noisy due to all the fans.
Anyways,
good luck. And be patient when you do the modifications, and it will look nice too.
-Paul
