I just spun a main bearing in my 420HP 454. I have a virgin Marine Power 330HP 454 that is not being used. I'm thinking about swapping the top end of the 420 over to the 330 engine. I do know that the 330 engine has 4 bolt mains. So my question is, would the 330 engine have the 7/16-rod bolts, steel crank and forged pistons like my 420 supposedly does? If not do you think that the 330 engine will hold up ok?
Thanks

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If it's the same as mercs 330 build:

So my question is, would the 330 engine have the 7/16-rod bolts
No, 3/8"
steel crank
No, Nodular iron
and forged pistons
No, cast and they'll be lower compression
like my 420 supposedly does? If not do you think that the 330 engine will hold up ok?
Yep, as long as you keep the rpms reasonable. 5000 rpm is pushing it.
Thanks

What year engines are these. They may be different generation which means heads will not swap without water leaks.

I suspect you might be asking for trouble. I know that having a "spare"motor is nice, but as already posted, I think the differences are many. I would rebuild the 420....

The 330 engine is about a 1991. It has been setting up since 1995. It's in a 3/4-ton 4X4 truck that had only about 20,000 miles put on it.