It makes sense that there wouldn't be a lot of difference in the BIOS at least. The routines contained inside are only for programming the sound, VDC, and input (mostly the VDC). Input and sound are the same, and video has the same programming commands in either region. The VDC uses 256 × 192 pixels no matter the actual vertical resolution of the TV. So the only thing that would have to change is delay values, and the BIOS has only one internal delay, the pause screen.
Eventually I'll get my diag shield in a state that I'm happy with, but even as is, it can read the BIOS through the expansion port. It currently just runs it through a CRC algorithm to make sure it checks out, but with a small change it could be made to dump the contents as a hex dump.
So are the above posted ROM files the official dumps? If so, I should add the PAL/SECAM one so it can compute the checksum there for comparison. I guess I also ought to at least print out the expected region.