I have been around this forum for a while, and I have not seen any alternative to the stock cap.  One member has welded in a new filler neck and used a different cap - but other than that we have all been using the stock cap.  Every nowt and then we get a question about the leakiy gasket and fuel running down the tank after a fill up - and unfortunately the rubber gasket is not available from Suzuki and we have to explore ways to get a gasket that will work.

If you want to cut out the old filler neck and install a new one - that is possible.  You can also weld a metal panel on the bottom and top of the speedometer cut out, and you could also weld up the old filler neck and put a new one in the center......that would be a new twist and it would get you another quart or two of fuel capacity!

I have thought about doing something new with the fuel cap but have not gotten that far yet. Please share what you do come up with.