68 dart GTS 18 rims question

So what did your brake conversion consist of? if its 73'-up front brakes and large bolt pattern rear axles and drums then the track of your car has widened over the stock 5x4 brakes, meaning you will need more positive offset. Your best bet is to measure your car or buy a Percy's Wheelrite. 18" will fit with the right tire and offset. I run a 17x7 with a 215/45/17 tire on the front and a 17x8 with a 245/45/17 rear. I don't recall my back spacing on the wheels but I did custom order them as I could not find any off the shelf rim to fit my car, which at the time was 73-up BBP converted and now has a Dr. Diff 13" front brake conversion.