I may have solved this mystery with the help of an answered question from a Summit Rep.

My engine was a TBI, but I no longer have it in my truck - it was replaced with an Edelbrock Performer Manifold. And according to Summit Racing, if I no longer have the Throttle Body unit, I could use heads designed for 1967-86 SBCs as the blocks for (1987-95) are identical.

Can anyone else confirm this?

Thanks