Hopcar- I just got home from the boat after fixing the tank. Please tell Peg thanks for the tip. I will save it for next time,
How the story ended.....
I struck out on finding someone to spin weld the fitting. Having welded plastic in the past, I decided to go for it with a heat gun. Realizing that the most fragile part of the fitting was the threads inside the fitting, I installed a 1.5" PVC plug
into the fitting. This would serve as a male form for the female threads and preserve them when the plastic got hot.
Since the wall for the old fitting was thinner than the new fitting, I had to ream out the hole in the tank. In the end, I had a nice, symmetric, smooth and virgin plastic hole.
The weld was a straight forward plastic tank weld. Much easier than I thought. The trick to doing them is to have either a plastic welding rod (lots of luck finding one) or a scrap from an old tank to use as a welding rod. The truly anal can cut the scrap piece into strips, I prefer just to use a corner of the panel.
I heated the outer edge of the flange part of the fitting until clear and used the extra material more to schmtuz (welding term) the edge of the fitting to meet some irregularities in the tank wall. During the course of doing the weld, it was obvious the threads were getting hot, so the plug
really saved me.
After the first pass, a visual inspection
of the weld showed two "areas of concern", I reheated the fitting and the extra material, adding a little material to fill those voids.
Once everything cooled off, the plug was a handy way to leak test the weld. I did not see or feel any leaks
Thanks to everyone for the inputs.