Hey, When I was restoring my 53 pickup, the gas tank had some rust in it, and who knows what else. My buddy and I took a chunk of airhose with a fitting for weight and stuck it down the guage hole, turned on the air and let it flop around loosening up any rust. We didn't use a vaccume as there might be a spark from the motor to set off any fumes. Then I bought a couple of kits for gas tank lining at NAPA store, followed the directions and it coated the inside. Haven't had any problems other than cramming expensive dinasours down the filler spout. Good luck.
