I was just messing around with the 2006 5.9 ECM I mentioned in post #2 and figured what the heck.
I had recently downloaded and modified (shut off the SKIM and other items) another ECM's O/S and re-flashed it, so I attempted to flash this one with the modified O/S and lo and behold, it apparently took it!
The only thing I can think of is the '1975 one was an old boot block, plus this it had NO VIN presenting, which is probably why it didn't tell me I needed a licence.
Unless I'm missing something?
All I know is it presents with a VIN and an O/S, when it didn't before my experimenting and it shows DTC codes, like it should on a bench harness, when it didn't before.
For the record, it was presenting the exact same errors as the 6.7 one above, P0161, Data Missing/Corrupted ($11).
I think I got stupid lucky.
One thing that is interesting to note, the Part Number on the O/S I flashed into this '1975 ECM was from a '7149 ECM, yet it retained the '1975 Part Number, but with the '7149's VIN and the modified O/S.
No wonder people go nuts working with these things.
Mark.