This wiki link will give you the lowdown on the original V6 engine...
https://en.wikipedia.org/wiki/GMC_V6_engine
These engines are still around over here, but getting scarce now
Have you figured out which small block engine you have in the truck...
Check passengers side ( for this truck, not your English gems!) front of the engine block for a set of stamped numbers ...if the block has been decked a couple of times it may be difficult to read...
Also look at the casting number, drivers side rear of block. That will tell us what core it is...