The Radius 81/110 uses the standard Mac video connector while the Mac 8100/110 had that funky Audio/Video/Microphone connector so they are not the same exact motherboard. Not sure if anything else is different.

The 9150 should have 5 slots just like the Quadra 950 (same case), 4 are Nubus and 1 is PDS. The 9150 is the only PPC machine with 4 Nubus slots.