According to the parts manual, the rheostat part number was changed in the middle of the 1967 150G model year.
Early 150G's (prior to serial number 15066623) used p/n 0713247-200. Cessna shows this superseded by AY 0713247-201, at $2,139.30 (Yingling Aviation... not a misprint)!
Late 150G's used XR 6085, superseded by S-1880-2, at $278.85 (also Yingling Aviation).
I haven't found anything on specifications yet, but I'll check my avionics manuals.
I agree that most LED's don't work well on dimmer circuits. They are are either on or off.
