This is getting interesting, because GM only started casting 5.0 and 5.7 on blocks cast after 86 when the block went through a redign that made it a one piece rear main seal and than a year or two later, roller cam capable.
What is the casting # at the back of the block ?
207, 638, 880 number will start with a 10 or 14.
I was going to mention you have a bunch of cheaper (and much better) head options as GM made a bunch of small chamber heads in the 10 years preceding the Vortec, combustion chambers very similar to the vortec with wall design and more centrally located spark plug. The 217 casting is one example.