427's are easy to ID by the cross-bolted mains, and if there is a oil gallery rib just above the oil pan (forget which side) it's a side-oiler.
If the date code of the block is 1965 or earlier than it can't be a 428, it's a 390 or 352.
428's are externally balanced so the flywheel will have a balance counterweight on it. 390 and 352 are internally balanced, so you have to pull the pan to take a look at the crank, and while you're there you can measure the bore.
That ought to be enough to tell whether you're looking at a 428 or not If it's a 410-390-352, they're probably all the same value (410 may be more).