Sam,

The W32 came original with a standard 35 gal Stbd tank and an optional 35 gal PORT tank. The optional Port tank would provide you with the 70 gal you desire. You should be able to have this fabricated locally with little trouble. This is probably a better solution than trying to replace the existing 35 gal Stbd tank with a single 70 (assuming that this tank is in good condition).

Certainly you could do an engine swap. But understand that this isn't an easy or inexpensive task. While my boat has the 51hp Perkins 4.108 option (as well as the 2nd fuel tank), the engine is now 36 yrs old. No doubt I'll be looking for either a rebuild or swap at some point as well.

As for water tankage, there were multiple options as well. Some came two 47-gal plastic tanks from "Inca Plastic" installed beneath the cabin sole. Others apparently came with a stainless tank, equal in dimension to the Stbd fuel tank and mounted on the Port side. I have not actually seen this configuration and the Factory Build Manual is not concise regarding the description thereof. But, based on the dimensions illustrated, I believe this is correct and likely the configuration that you reference, based on your questions.

Hope that helps.

Jack