I've got a Honda TL250 (1975) Service manual for sale for $30 plus postage.
Send me a PM or email if you want it.
It's also on eBay (more expensive)....
Cheers,
Joe

I've used several different brands, successfully long-term.
The issue is however that the tank needs to be PERFECTLY clean inside! This is usually achieved with thorough mechanical derusting if required - e.g. fill with gravel, wrap in thick blanket or bubblewrap and put in cement mixer for a couple ...