Originally Posted by 1badLemans
If all else fails pull the intake off and the "400" or the "350" will be cast into the lifter valley and be plain as day.
"00" would be for a 400, "50" for a 350, and "55" for a 455. They didn't cast the whole number in the lifter galley. The easiest thing is to get the block casting number or the block date code & the block code that is stamped into the front of the block just under the passenger side head. Post those numbers and we can tell you exactly what you have.