I'm with you on the gas tank issue. I'm currently combing through aliexpress, there are options but guessing how it will mount is a bit of trick. Small pit bike metal tanks for around $90, or plastic options $50 and less
Been using a 460 for years. First was axle mounted chain drive, then rack mounted spindle. Finally the center mounted 8 speed that breaks derailleurs and chains. Need an IGH and beefy chain. I bet that saton will hold up. You may need to strengthen the mounts fot it though. Good looking build bud!