I just haven't ever seen a V8 after 86 that wasn't a vortec with center bolt valve covers......pete
Actually the center bolt valve covers where put on GM engines across the board.(there answer to there leaky 4 bolt design).
My 89 GMC is a throttle body van.Non vortec.
I also had a 95 GMC pickup there that was also a 5.7 throttle body engine.Again non Vortec
GM treated the Vortec like a performance option.They put a bunch of them in S10 pick ups,Blazers and a bunch of cars.
I am pretty sure of you had the right sales man you could have ordered a Vortec engine in any of there trucks vans.allot of people just opted not to order for what ever reason.
I have an 05 Extreme Blazer here that has a Vortec 4.3 in it.This engine also has an aluminum oil pan on it.It is TBI injected......
I am by no means a Vortec expert.I just have owned enough GMs over the past years to know the difference
........Wookee