73 duster 17" or 18" wheels ?

I like 17's and 18's. :-)

The easiest setup, in my opinion is a 245/45R17 in the front and a 275/40R18 in the rear. The Duster seems to look better to me with a little bigger wheel in the rear, but this setup give's the same sidewall depth's for a little more uniform look, if you like the pro-touring style.

Only issue with these tire sizes is you can't rotate them, front to back.

Bonus is, this is a common Vette tire combination, so finding tires should be easy.

In the front, you should be ale to run a 17x8 with a +30mm offset off a late 90's Mustang. The rear is going to require either a wider rear axle, or a custom wheel. Like above, you will need to measure your car to see, though, for both ends.