Could he just replace the PROM chip?
The 27SF512 flash chip is a 28 pin EEPROM, the original 24 pin EPROM chips from then had to be IR erased and "burned", some guys over on GearHeadEFI still have the equipment to do it. The Moates Burn2 can read them but can't "burn" them. So, you'll need to adapt your Mem Cal socket to accept them. I THINK! I have a 7747 ECM that I had a ZIF (Zero Insertion Force) socket installed in it so I could flash my own calibrations.
You must be registered for see images attach
You must be registered for see images attach
Here's another link that shows the 1199 AND the 6396 but no chip (probably was the 27C512) maybe the definitions for the 6396 will work for the 1199?
https://xtronics.com/wiki/GM_ECU_eproms.html