GM Flywheel Casting # Question

Any casting number gurus out there?

I've got a GM flywheel w/the following sets of #s casted into it.

973456N
G245
GM3

Any idea if that's 350 or 400?

I was gonna use the flywheel we had on a 350 and put it on a 400 (w/a balancing plate), BUT the bolt pattern on the 350 is too small (late model 350 flywheel, older 400).

I have this other flywheel (w/the casting numbers above), and the bolt pattern does fit. But, I want to be sure what it was on originally to tell whether I need the balance plate or not (don't want to screw that up). I'm 90% sure it was from a 350, but want to be 100% sure before I throw anything out of balance.

Thanks ....