[R&B51]

Thanks for replies. This gas tank thing seems to be a complicated subject. I see what has worked and what you're having troubles with. I really wanna try to have my cake and eat it too, so will try to find/fab a tank to save spare space. Saw two possibilities, cheapest is a long skinny tank inside frame beside drive shaft. I measured the space in front of rear end between frame and old drive shaft and 14" wide x 60" long and depth is determined by ground clearance. Not sure what minimum should be-how far below frame rail is safe. Drive shaft would hit before tank if tank was about 8-10". This is closest prefab tank I could find and 11" depth (if it is 14" wide and 11" deep" and not other way) is one concern and 14" width only gives an inch to clear driveshaft. Shaft doesn't move side to side. Could install heavy steel safety plate between it and shaft.
Anybody seen this done?
Here's tank info off Raybuck: 81973-81 C/K Series Chevy/GMC Fullsize Pickup Ahead Of Rear Axle 20gal.
Dimensions: 56" x 14" x 11"
Strap Set: ST01