I just finished my 6540 / 6550 test for the PET 2001
I had some trouble with the 6540-ROMs in my PETs and built an special adapter to read them in my EPROM-burner.
But it's not possible to read them in my TL866, Merlin/Promenade C1 and the Tiny Eprommer :(
The 6540 need a clock to operate correctly!
I decided to code a test-kernal that verifies the 8-bit-checksums in the PET ;)
Also I appended a RAM-test for the whole 8kB.