Thanks guys, I am having fun.
About the fins, I just drilled two extra holes in the top fin and the tapped in threads. Used stainless steel threaded rod and built the fins on them. I probably should have used a jig for uniformity but did not. I am not much for measuring either. So I just cut some brass pieces from the hardware store one at a time. The top piece is considerably thicker than the lower one. They are not too uniform bit I think id adds to the look.LOL...
I think I have the tank the way I want it now. I like the look behind the seat as opposed to the stock tank.
I welded the back drop outs to each other and to the frame. I only did it on the inside for appearances. I also spot welded the all the grade 8 nuts and bolt together so no wobble out problems.
I had made the four inch tank first and found it too large for the "chopper" so I put it on my "Speedster" looks better, ya?
The trick to using PVC for tanks is they must be lined with a quality gas tak sealer. I have had these filled for over a week and no problems. That stuff seems rally tough.
Cheers!