You are right, too big without cutting filler tube
I replaced mine about 5 years ago. I used a smaller tank, one which was not as tall. It holds about 12 gallons, I know its not much, but I only use 6 gallons a year. The yanmar is very good on fuel. If I ever take her to the coast, I'll install a second tank to increase range or I'll use extra portable tanks.Very pleased with mine, I had to relocate my filler since the tank I ordered had a different location for the filler tube. Custom tanks cost about 3x as much as one that is standard. Just use a hacksaw to cut some of the tube off to fit it through the cockpit locker opening.