i dont think a 35 gal will. isnt the tank on ur PW now in front of the rear axle? a 35 gal goes from frame rail to frame rail, so u would have to mount it behind the rear axle. not sure about an 18 gal tank though.
I know a gas tank from a 81-87 (carb) RC gas tank will fit in a 70s power wagon. Look at my project Heavy Hauler. I put a RC gas tank with all the brackets in the rear of the frame. There are pics on my site.
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