Alien tanks and axed tanks are the same thing, cut up fat bobs, skinnied up and welded together. The originals from the 70's have a slightly raised ridge down the center, and usually have either Paughco or GME stamped on the tabs and hold 1.8 gallons. The repops have no ridge down the center and have a slightly larger capacity. The axed/alien tanks are just as tall as they are wide. The mustang tanks were never as tall as the axed tanks and were a little wider so they had a flatter look to them.