1974 Duster wheels & tire size

Not to sound like a jerk, but are you sure that you have small bolt pattern wheels? After 1972, Abodies all came with LBP wheels and disc brakes up front.
There were some models in 1973 that used some leftover drum assemblies for the font wheels, but I've never heard of a 1974 having front drums.

With a stock A-body 8-1/4" rear, 3.5" or 4" of backspacing will suit you well. You might be able to pull off 4.5" backspacing, but that will put the tire very close to the spring perches. It depends what kind of tire you run.

You can go a bit wider on a duster than you can on a dart, but I think a 255/60R/15 will fit well on the rear. With this tire, I would not run more than 4" of backspacing on the wheel. I believe most stock 15" x 7" steelies have ~4" of backspacing, but you will need to check with somebody else to confirm that.

For the front, you can still run a 15x7 but you will be better off running a 225/60R15 or 225/70R15. This will provide better clearance up front with the steering at full-lock while still giving you decent traction.

Also, welcome to FABO!

-Mike
no they didn't. DISC brake cars were LBP after '72. DRUM brake cars were SBP to the end. DISC brakes weren't mandated by the federal gov't/NHTSA until cars built after Jan1 1976. my 1976 duster (build date 11/75) has 10" drums up front, SBP 7.25" with 3.23's in the rear (iron case A833OD tranny stock).

most stock chrysler rims are +1/4" to +1/2" offset (stock 15x7 steelies on an M body are +1/4", which gives 4.25" backspace. my stock SBP ralleyes are 5.5 with 3.75" backspace, which makes them +1/2" offset

front wheels about the biggest diameter you can go with is about 25.5" before you start running into issues, especially the leading edge of the front fender when turning. the back you can go 28".