Does anyone know if the 90's era 454 engines out of the half ton trucks are strong enough or the cylinder walls thick enough to use for high horsepower setups. I figured the TBI 454's would be the only big blocks I could find at the junkyard.

I heard something about the coolant passage holes on the later style blocks may be oversized as compared to earlier style blocks. Maybe causing interference with aftermarket heads.

Modern aftermarket heads tend to be "universal" in that they will work on Mark IV, Gen 5 or Gen 6 engines. It's the stock heads that tend to be the problem.

1990 and earlier engines are Mk IV. Most have series flow cooling, but some have parallel flow.

'91 to '95 engines are considered "Gen 5", and have parallel-flow coolant routing. You cannot bolt on earlier "Mark IV" heads without the possibility of coolant seepage into the lifter valley. There are special head gaskets (a left side # 4923 and a right side #4918) from Victor Reinz to ease this conversion.

'96-up 454s are considered Gen 6, they also have parallel-flow coolant routing, and will accept any older heads--Gen 5 or Mk IV. No need for "special" head gaskets except that you'll want gaskets that allow parallel-flow coolant routing.

Do a search on this site for coolant routing (series/parallel)

I have heard the Gen 6 block is weak, but I have zero experience with it.