The model number of the tank from Karma is FMT-30-BPM. The replacement tank will be of a thicker gauge and will be painted, no doubt to reduce the opportunity for corrosion.
I've posted the pictures that I took during removal at this link: Picasa Web Albums - SailingCal21 - O'Day 34 Fuel...
I'm really interested in the source of your leak on the tank. Please post pics...before you chop it up
Short Pump, VA
1981 O'Day 34
"No matter where you go, there you are."