If its got an ECM controlled efi system (probably throttle body EFI) and no ecm, there was a place that could repair these, maybe you can contact them & see if they have spares.
Otherwise, see what intake you have, you might be able to simply convert back to a simpler (and better IMO) carbed engine. You'd need a carb style intake, and a low pressure electric pump, unless using a pre-Vortec engine then its even better you get to use a cheap and reliable Carter mechanical pump.
I'd take the opportunity to go with a nice 4bb, Edelbrock is easier if you have a Merc. Carbed engines are not subject to Merc's making parts NLA. Because all is available from Edelbrock & Holley, pumps from Carter. I can even get just about any part I need for a Quadrajet that hasn't been made in over 30 years.
