Make sure the bottom of the tank is cleared enough to fit over the frame tubes.
I did not have a tank for my BW and had a very hard time finding something to fit because the frame tubes require a big wide tunnel to fit over.Most bikes have these tubes farther back so the tunnel in the tank can be narrow.
My tank is steel because I used a torch to reshape the underside of the tank to fit over the frame.
If anyone find an aftermarket tank that does fit,please post because I need a bigger tank!!!