I was looking to put some vortec heads on my 91 350 TBI Blazer and noticed(on EBay) that there are different castings. Is one casting better than another? Would I be looking for something specific because I'm putting them in a truck verses a car?

I run 35" Super Swamper tires with 4.56 gears with a detroit locker and a 700r4 my engine is mostly stock

 

Yes, there are different castings of the vortec head. The exhaust ports on some of earlier heads have a restriction caused by the valve seat protruding too far into the opening. By doing some minor bowl work they are easy to clean up. The 96 and later vortec heads in stock form, of any casting number, with no porting, still flow tons better than the stock swirl port heads that came on all sb tbi engines.

Steve