Got Eville's tank sorted, just have to weld the bungs for the rubber mounts in.
These represent 3 hours of my day to get to where I wanted them. Standard 5/16 18tpi shouldered bungs don't have a large enough diameter on the shoulder area to support a standard tank rubber mount correctly so I made some. I could have run a washer instead but that would've bugged me.
Smallest gas cap and bung I've ever seen, a gas pump just fits in. You'll know it's full when gas shoots out the top of the tank.