Just have removed both fuel tanks from outboard of our twin Perkins 6.354. My son did the first with my cheerleading. The Marina did the second with a primary and a helper.
At my suggestion, my son did the first with a 4-1/2" angle grinder equipped with cutoff wheels. He cut 1/3 of the face out, then cut the first third of the tank. He had to cut a slice in the tank, horizontally, to collapse it in height before it would make it out over the stringer and the exhaust. He then crawled into the space where the 1/3 came out and cut out the baffle. Then cut the second third from the remaining 1/3 and cut it in half horizontally. Those two sixths came out without much effort. He then cut the remaining third in half horizontally and those two sixths came out. Generally, the loose pieces would cheerfully catch on each other and fight him mightily!
These TTs have got the wood frame with 1/4" underlayment plywood and ceiling tile coverings. We removed all the coverings but left some of the wood frame in place.
The Marina fellow took all the wood framing out which allowed the tank to slide away from the side of the boat. He nibbled pieces of tank out using a Sawzall and sabre saw. He did some with the cutoff wheel. When he'd finally got the aft 1/3 out he cut the remaining 2/3s horizontally and they came out. Because he removed the cover framing, his helper could watch to see where the Sawzall blade was going. No damage was done to the boat.
The original tanks were about 180 gal., ea. We're putting back tanks that are about 80 gal ea., thus the chatter elsewhere on this Forum about range and fuel use. See my posts on the subject.
