Identifying a 400 flywheel

[Jimal]

While poking around underneath my recently purchased '65 K10 I discovered that the engine is a 400, not a 350 as the seller indicated. Not the worst thing in the world, but assuming the guy I bought it from didn't know what he had, he probably just reused the flywheel off the 327 he pulled out of the truck (and now sits in my garage).

I'm assuming that the engine came out of the same '75 pickup that a bunch of the upgrades this truck has came from. Should I be able to tell from a visual inspection of the flywheel (without taking things apart) whether the flywheel is correct or not?