anyone ever install a t56 into a thirdgen with a 427 big block?

wouldn't be any different than putting it behind a small block. Hell, even the flywheel would be the same with a 427.

T56 flywheel is for a one piece rear seal crank. 427 uses a 2 piece seal.

You need a special flywheel. The 427 is internally balanced. Normally they're installed on a 454+ which is externally balanced although an internally balanced crank can be purchased in the aftermarket.

It's a Chevrolet V8.... it's all exactly the same. No difference in any way.

Keep in mind, you'll probably have to drill the late-model (78 or so on up) starter bolt hole, and of course you'll need a "conversion" flywheel such as the Centerforce 700107. Just like any mid-70s or earlier small block.

A piece of advice: have your machine shop drill the starter bolt hole before you put the motor in the car!! Don't believe anybody that tells you that this that or the other starter "ought to" work; it won't. You need the right bolt hole, period.

...it's kinda funny, as many motors as I've built/installed/etc I've never ran into one that didn't have both start hole lay-outs. I've heard of it plenty, but never had the issue myself. - good point sofa

yep, you'll need an internally balanced flywheel for a 2-piece chevy.