R100R tank

[awaffa2003]

will an R100R tank fit the R65, can i make it fit?

[Rob Valdez 79 R65]

R65's from 1978-1984 had a mounting system unique from the larger bikes.  The exception being the R80/100GS and the R80ST.

R100R sounds like a post-85 bike, and I am not sure what kind of fittings they had.

Then length and matchup with the leading edge of your seat is a whole nuther subject.

Of course, anything can be made to work.  And I believe the front mount is pretty much the same from /5 on.