I'd guess the PPC and BVision would add a bit of heat. But, with a couple of well placed fans/vents that might not be a problem (besides the added noise). I have the following in my A1200 desktop with no heat problems and it runs silently.
Blizzard 1260/060-50MHz
Blizzard SCSI IV
128M RAM
ScanMagic SD/FF Internal
4xIDE'99
20GB 2.5" HD
HD Floppy
I'm considering the Subway or a Delfina card for the clock port. But, I've promised myself I wouldn't throw any more money into this box.