Re: Tank petcock
The Yamaha petcock would be pretty easy since you can find it almost anywhere...
To do this you would create three holes in your tank. For the gasket to work, you need to tighten the screws more than the un reinforced sheet metal will allow. You just need to use a lot of epoxy where it mates to the tank as well as screws.
This is just the way I see it going in my mind. There is probably a better way still, just throwing it out there.