Um… buy larger wheels with the 4 x 4.5″ bolt pattern.
Wheel Vintiques sells new 15″ wheels with that pattern. Many cars used the 4 x 4.5″ bolt pattern, including six cylinder versions of the early Falcon, Comet, Mustang, and Maverick. I have 14″ aluminum slot mags on my 62 that were originally on an early 60s Mustang. FYI, the Mustang II and later Mustangs do NOT use that same bolt pattern and those wheels do not fit.