John,
I would go with the two pound density.I believe this is what was used in the original builds,and is the most common pour foam stocked by most fiberglass dealers.
The structural strength came from the fiberglass boxes laminated into the hull.The foam is there for flotation and to displace air so that any water can't fill that space,and sink the boat.(just my opinion).
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All this,just for a boat ride
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