Good morningjclays, the raw water cooled engine plumbing has undergone many changes since the old days. It is actually more efficient now days.
If this was my boat, I would rid myself of that old and odd style plumbing and I would re-configure it into a more modern style.
You would have fewer issues (if any) and it would simplify things for you.
Regarding your post # 29..... No expensive OEM parts...... no hunting for NLA parts....... no machine shop modifications....... and so on!
Do it once, and don't look back!
Just a thought!
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The only thing keeping me from upgrading is the intake manifolds. I haven't seen any of the newer ones that have a profile as low as the old ones on my boat. I currently only have about one inch from the bottom of the closed deck hatch to the top of my flame arrestor. I dont want a raised deck or hump to accommodate a higher rise on the intake manifold.