4in vs 4.5in bolt circle rear axle

I am a Mopar nut , by junk and build it . The avatar is my 500 stroker kicking A### at Road america , yep a BB
My present project is a 68 Cuda notchback
Thanks for all of the replies
I am going to change axles to a 4.5 bolt circle .
what is the easiest most inexpensive way to do this ?