you would need wheel spacers or a wider diff. to figure out how big of a spacer you need you will need to mount the tires on the wheels and place them in the wheelwell. then measure the distance between the wheel and the face of the drum. what size wheel and tire are you looking at?
that is a good price. usually people run late model mustang wheels with a 1" spacer. to fit 275/60-15s you need to get the spaceing just right.
Simple math. If the max BS possible in our cars is 4.5 Then 5.75 will require 1.25" spacer. The problem with old cars is that no two are the same. Some will have fitment issues, and some wont. What ive done before buying spacers is to cut some 5/8" round bar stock and mount the wheels with that. You can play around with different lenghts to see which fits best. Then you can figure out the right spacers to buy.