I have an old Bertram that has a pair of 454's which I will either
convert to diesel or probably scrap. The local Junkyard says that I
ought to look into converting the GM Isuzu Duramax because they are
relatively cheap, as there is little used demand for them. However,
the Duramax is an electronic engine. Is this a bad thing in terms of
waterproofing and mounting the boxes, or is this actually a pretty
good idea?

I already sold the 454's to local street rod guys and I put the
marine manifolds and hardware on EBay, so there's no going back.