i just pulled apart one of my 89' Mark IV 454 magnum engines in-order to re-bearing and re-ring it ... im pretty sure the crank has never been machined or cut down and usually the back side of the main and rod bearings have markings that tell what cut the crank has.... the markings on the back of the rod bearing are as follows..........
GM4
2621313
126A 82

the fact that they are stamped GM4 leads me to think that they are GM gen. 4 factory bearings which would also indicate an un-cut crank... what do you guys think....

ps. the other engine was stuck and was removed and is being completely re-done !
the engine in question above was a good running engine but i figured i would freshen it up while my other engine was being rehabbed !

take a minute and a micrometer and measure it. never guess when you can actually know the answer. you are going to need that info for clearancing anyway.

Yeah, you need to take a mic to all the journals in 3 spots anyway to figure out if it needs to be cut or polished, then the specs will tell the tale.

Do it, measure all journals. I just started the same project. Crank was close to .0025 out front to rear. Looked good with plasti gauge but torqued main caps/ with bearings in and subtracted difference from crank and the clearances were enough to make me send the crank out for cutting. there is a thread on this I posted and everyone had some valuable info/charts . in this section. good luck Cort