So at the end:
- if you want to use KS 1.3/2.04/3.1 on old rev.5 motherboards you have to rewire pin 1 of the ROM to pin 31 of the socket, and put Vcc (5V) on pin 31 of the ROM (maybe some kohm resistor is not a bad idea, to limit current).
- if you want to use KS 1.2 on rev.6a/7/8 motherboards you have to rewire pin 31 of the ROM to pin 1.
Kickstart 1.3 is 256k, the same as kickstart 1.2. So you don't have to do anything special to upgrade. You should also be able to put a kickstart 1.2 chip straight onto a rev 6/7/8 motherboard without doing anything.
The problem was caused by commodore receiving incorrect information when designing the motherboards for 512k rom chips, which meant one of the address lines was wired to the wrong pin. You can fix it either on the motherboard or the rom. The official kickstart chips came with a wire connecting pin 1 to 31.
My revision 5 a500 shipped with kickstart 1.3 and it requires the pin 1 to 31 mod to work with 2.04 or 3.1
