I ran into a deal locally for a late 80's GM crate 454 for a great price. My question is does anyone here have any experience with or know the specs on one of these? It's a Mark IV engine and it has the original aluminum intake and valve covers on it. I'm guessing it's the same engine that Chevy put in the 1990 model Chevy SS454 pickups because it looks exactly like one. Do these have the oval port heads on them or are they like the newer crate 454's and have the rectangular ports? Any help appreciated!

It could be the LS-6 crate motor.If so,its a solid flat tappet cam with rectangular port heads,(open chamber).Look for XAA in the engine #.
Guy

If it is the same as the SS motors you will find peanut port heads with a flat tappit cam
These had CI manifolds not Alum.
They are great stump puller but run out of breath by 5000 rpm.
You really need to pull the numbers to know what you have for sure

There is a machined area on the block just above the timing cover, you will see a suffix code located there, record this and all other cast numbers and dates you can find, post everything you find, to get the correct feedback.

Thanks guys - will do.