I got to check out these ROMs. The FPD and TPD hardware is completely identical except for the resolution (640x870 for FPD, 1152x864 for TPD), and also identical to the later ASIC-based version of the cards. ROMs from the later 1991 632-0022-A1 ASIC-based board will likely work fine on these older cards in case a newer version turns up on one of those cards. The 1991 board ROM labels are of the form "(c) 1991 Radius TPD/FPD-ASIC U6 297-0204-A V 4.1 256K".
Both cards use the $C00000-$C7FFFF space (ROM at $C00000, 256K of VRAM at $C40000, read $C20000 to enable generating IRQ 2 for vblank, read $C10000 to clear the vblank IRQ), and both cards check for the SE Accelerator's ROM signature at $C80000. The SE Accelerator also checks for a Radius video card ROM at $C00000. Both video cards and the SE Accelerator have a "by Andy Hertzfeld" signature in the ROM.
The incompatibility with System 7 is because System 6 doesn't touch the vector table from how the system ROM sets it up, so when the Radius ROM changes the IRQ 2 handler it stays put. System 7 overwrites the entire vector table and its IRQ 2 handler assumes a Mac II or later machine where IRQ2 comes from VIA2. (This doesn't hurt the Plus/SE/Classic because normally they never generate IRQ 2). So when a VBL IRQ fires, the handler doesn't know how to clear it and the 68K is stuck trying to service IRQ 2 forever. It might be possible to patch the ROMs to fix that if the later official fix version from Radius doesn't turn up.
