Actually, any tank will fit. The /7 tank is longer from the steering head to the seat and an earlier tank will fit but there will be a gap between the tank and seat if you install an earlier tank.

Cool, thanks! Is that across the line? Tanks for r80s/r90s etc would fit?

Admission of error. I was thinking of /5 and /6 tanks, both regular and large versions. Then the more sculpted, contoured later tanks like the one that came with your /7. R65 tanks, maybe. G/S and GS tanks, less likely. More specificly, you will need to limit your search to models with the front brake master cylinder under the fuel tank if your R75/7 is still equipped with that feature. A /6 tank has the extra room on the underside for the master cylinder. The /5 tanks do not. An R90S tank should fit. I regret any confusion that may have originated with the first response.

No worries, and thanks for clarifying!

I had the same problem with my R75/7 . All the tanks I found were as bad as mine or cost more than I paid for the whole bike. I finally bought a tank from India on ebay. The tank came in polished aluminum. Steele tanks are also available. I wanted the original color so I had the beautiful polished aluminum pained . I had to make a small dent under the tank to make it fit perfectly. Also the stock gas cap would not fit . The Indian made tanks are set up for a Monza flip top cap. All together tank , having it painted , new emblems , and Monza cap , I spent over $600 .

Yeah, that's what I'm trying to avoid. May come down to it, though.

Got a pic of the bike you can share?