A '79 T'bird shouldn't have any spring perches on the rearend...it's a Fox body and the spring sets into the lower control arm and the rearend just has brackets on it..no perches...must be some other year. Unless you are building a truck, which you didn't mention, the Bronco axles will also need the pattern on the flange changed...they are the big pattern....I think 5 on 5. The cost to have both the cutting,splining and new pattern ( whcih I think requires the flange o.d. to be reduced for regular brakes) would probably cost as much(or more) as a set of axles from several places.
I didn't make note of your location, but I think that Currie has re-cut Ford axles for about $250/pr
EDIT: My mistake..the Fox body 'bird wasn't until 1980.