I remember someone doing it, they drained and cut the old tanks to get them out, then had two tanks made with very short hoses joining them that went in place of the single side tanks.
Not sure what thread that was, but they won't chime in unless they happen across this. I'd suggest sending them a PM.
I’ve reached out and awaiting a response. I did speak to someone who worked for Ocean and they said replacement is doable with engines in place and tanks built to factory spec.
Did a 46 1985 years ago. Unbolted engine and a-framed to center stringers. Removed Exhaust hose ,pulled tank out opening. did one side at a time. Purchased new tanks from Ocean Yachts but the came from south Florida. Sorry can't remember the name of the company.
Oh yes the tanks were supposed to be a-fixed to the hull bottom. Port side was not - causing the leak, came right out. Starboard side was glued in tight thought we were going to rip the bottom of the hull out when it popped free. Starboard was not leaking but did both any way. Oh yes rebuild the air intakes while you are there only access you will ever get.
Thanks for the info. I did find someone out of jersey that used to work for Ocean that can replace them without moving the engines. I ended up passing on the boat because it was not as advertised and complete mess, basically a floating condo for 30 years. Still looking for a 3 state room 48 or even a 45