Ayuh,...... Pull 'em, 'n send 'em to a machine shop for a rebuild,....
The machine shop will tell ya whether they can be saved, or are junk,.....
If there is that much rust in the head(s), what does the block look like. Pull the heads since they must be pulled anyway. Depending on how much water was in the block and its condition, you may have a 10 year old but new anchor. If there was water in the engine and it was allowed to freeze -- well -- you know the result of that scenario.
How hard is it to pull & re install an engine in a boat. It almost looks easier than doing a car swap.
Ayuh,..... It is easier than automotive,....
Ya ain't said what ya got, but the general sequence is, pull the drive, pull the motor,....
Reinstall the motor, align the motor, reinstall the drive, go boatin',....
1978 Mark Twain 351W OMC
Ayuh,.... In that case, ya got a Stringer drive,..... Forget what I said above, I was thinkin' ya have a Cobra drive,....
Ayuh,.... I don't do stringer drives, unless yankin' 'em, 'n junkin' 'em,.....
Southkogs is My "GoTo" guy for Stringers,....