I'd sure like to get the EE,adx working for the 94-95 LT1 engines. It connects and gets some data, some wrong data and some NO data...
I assume you know ...

'94 & '95 were the transition years from OBDI and OBDII. Some people refer to it as OBD 1.5. This could be why you are seeing so many data streams.

Checksum is a value calculated from the data that is pasted onto the end of a data stream by the sender. The receiver recalculates the value to compare to the sent checksum. This way the receiver can tell if the data was sent correctly or was corrupted on the wire.

I read calculating the checksum as you sum up all the data. Discard any bits that flow out of the 8 bit value then flip the bit values: 0 to 1 & 1 to 0. ( Called one's compliment. )
0xF4 + 0x56 + 0x01 = 0x14B chopping = 0x4B complimenting = 0xB4
Same result as Luke Skaff's pdf page 21
I'm not sure were the idea of the 0xFF entered the picture. Seems to be a red herring.

Robert