Vintage spyder that is
Then, no on the big tank. I have a Vintage Spyder. Stock tank room ONLY unless you have a custom one made. Since yours is all dented, how are you on fabrication? You could keep the bottom of the tank and custom make the top half making it larger that way. No room underneath and not much up top, believe me I know...
The stock size tank seems to be plenty though. I go 160 miles on a tank and a stretch is not a bad idea at that point. The car is quite comfortable for me, but after a couple hours in anything a break is good. The bladder must be paid heed.