gotta replace 7.4 liter - 502?

It's a GM Mk IV 7.4 Liter with a cracked block - A certain carburated GM 502 is going to appear here tomorrow. I have a week to evaluate it. The guy smashed the OMC King Kobra completely off the 502 boat. Two of his pals tied a-beam either side, and helped bail and towed him back - Water in the boat was 'bout up to the valve covers. A week later, the boat's in a 'friend's shop, he goes and fires the engine. Lights off and runs, life is good. 3 days after that, he goes back, lights it off, gets a huge ass-end crash, w/cracked bellhousing, motor jams and stops... I'm thinkin' the starter crash just made the engine cheaper, as I don't think I need his flywheel, bellhousing, or starter, and know I don't need the coupler, as I got Bravo1 with all that. Let's say they are both Mk IVs - Do I have to get a balanced flywheel for the 502 if it's scragged, or can I bolt my 7.4 L right up? I worry because they are externally balanced cranks, and I'm a flatheaded

rookie.

manual 16 bib block engines
might be some info in here

I appreciate the response, Bt Doctor - seems the guy with the 502 doesn't want to return calls, and is acting sqirrelly. I'm now going to go check out an '86 motorhome 454. It purports to have 48,000 miles on it. More than I'd like, but it's $800, what the hey... I'll post again when I know more.