my one buddy used a 205-60-15 on a 7" rim with a 4 1/2"bs for a 72 duster with a factory disc conversion.
the car is lowered a bit with the torsion bars, and the 205's clear by about 3/8" on the front, lower wheel opening.
that size tire fills the opening very well.
i don't know if a 70 duster has the same shaped opening or not, and i don't know how much taller a 235 would be.