It's another you didn't hear it run, or see a video of it running... I'd start it if possible.
At the least I'd leakdown test it before thinking disassembly.
What I don't get though, to be honest, is between the vortec you bought. And now this lt1, you're over halfway to a 100% brand new gm crate 350/290hp that you could then swap heads and cam to push closer to mid 300s. It would've been a direct drop in and wouldn't need fuel system upgrades.
It's a lot, I mean a LOT of money just to get an obsolete lt1 that parts are drying up for (optispark) before you even refresh the motor.
4l60e is junk. I'd never bother with all the effort of putting one into a car, and I'd prefer not to buy anything with one but would switch to a 4l80 if it did. 200-4R can be built better cheaper if OD is a must, as a bonus it needs no electric computer controller.