Originally Posted by
MILD THUNDER
Yep. The #3 propshaft tapers down right were it comes out of the lower housing. Similar to how a TRS or Bravo propshaft would. The 3A, like he says, has no taper. Just a straight big shaft.
I honestly wouldn't bother even trying to fire that other engine. Even if it does start and run, I wouldn't trust it for long. The seals are more than likely dried up, rings could be rusted, valvesprings weak, etc.
Now, not to say that its junk though. I would remove the engine, and tear it down. If the blocks are not toast from salt, or the heads, then I'd say just rebuild/freshen it. The 420HP Merc was a great engine, and also very easy to duplicate. You can find a older Mark IV 454 block, plenty of those around from hotrodders, old surburbans and pickups, etc. The crankshafts and dimple rods are good GM forged steel units. Also can be found for real cheap. The camshafts were crane, but alot of guys have used the cheaper "sealed Power" replacement cams. They offer some nice cams that are very comparable to the original 420HP crane cam, but about half the cost. The cylinder heads are GM rectangle port heads. These can also be found used/rebuilt for cheap. Same for the intake manifolds. Carb is your basic holley 800CFM double pumper.
What I am getting at, is that sure you can just order some 502 crate engines, probably have around 12-15k in them by the time you dress them with carbs, ignitions, accessories, etc. But I think it would be cool, and cost effective, to restore the boat with the original 454/420HP mills, GIL exhaust, and everything period correct. Granted it might only be a 60mph boat, but....still cool none the less. Now, If you really wanna get silly, you can while rebuilding the engines, build them with the intention of adding a supercharger down the road. Some good headgaskets, dished pistons, better rod bolts and head studs, and a cam ground on a 114LSA. Little things that dont cost that much more. Then once you get her running, a few years down the road, if you feel the need to go fast, you can bolt on some 250/256 blowers, and gain 10+mph!