70 Disc vs 73 disc

we have been gathering parts to rebuild a 70 Dart Swinger

If we change out the K-H brakes for the 73 Disc,
Since it needs front-end work anyway
Will the tire track width change, (be Wider)

want to use 15 x 7 all the way around
have all the parts to do the job

14" performance tires seem harder to find lately