I think that you are in for a somewhat hard hunt.
1) Your front track is now a bit wider, and the wheel centerline needs to compensate for that, else a wider than stock wheel, or a taller than stock tire, will rub on the fenders. But, if you bring it in just a hair too far, either the tire or the wheel, will rub on stuff.
2) on the back is a different deal; The springs are "in" the wheel well, and the fenders have wide lips. These two deals conspire to limit your tire selection, which limits your wheel width, and sooner or later, the offset/backspace will need to be changed.
3) therefore, I highly recommend that you install and fit, one factory wheel and tire, at each corner, in turn, and measure exactly what fits in there. Factory steel wheels can be widened and or the spiders can be moved.
4) alternatively, you can search the comments and see what success stories are out there. 67>75 Darts are a bit of a struggle to find aftermarket wide wheels for, as are all small-tub Mopars.
5) if you are fitting 15s or less, pay attention to the UBJ clearance to the wheel, at full suspension droop and throughout the wheel's turning motion. Leave room for wheel-weights, and for body sway during cornering, and for sidewall-deflection, and don't forget that when braking hard, that stinking body is coming down, down, down, and your tires better be duck, duck, ducking.
6) the time you spend getting it right, will be well worth it when everything you spent money on, and especially the stinking shipping, actually fits and runs.
