In 86; the SB frame and 4runner were the same length;LB and Xtracab longer frame.
The SB frame was 17.3 gallons, LB frame 19.2.
Maybe latter 4 door 4runners had longer frame...........
All of the 1st-3rd gen 4-Runners were made on the short wheel base frames. It would have made more sense to use the long bed frames for more rear seat legroom, but then again they weren't being only built for the U.S. market.
Caboose
Another cheaper option to consider might be replacing the current 12gl. oem tank w/ a larger 17gl. one from a 2nd gen 4x4. It might not be a direct bolt -in, but it should fit. I know the 1st and 2nd gen truck wheel bases are the same, I used a 7' bed from an '80 truck to replace the damaged bed on my Dad's '86.l The bed fit almost perfectly, I only had to adjust the mounts a little to get the bed to fit as close to the cab, as the original bed. Seeing how the beds interchange, I don't see why a larger tank wouldn't fit. You might even be able to squeeze a 19gl. one in there.
