My road bike is a 92 Paramount (7 speed downtube originally) which I refitted with a 50/34 compact and a 12-32 rear with an XT rear D/R. With 9 speed Ultegra it shifts flawlessly.
That's my solution to old knee, one of which is metal, and Texas hill country.
It's a simple thing to change rear cassette and rear D/r, and probably cheaper than a new crank.
Just sayin'......