Narrowing an 8 1/4" rear end, how is it done?

Geez, every time I go to do something, it seems like it turns into a dive down a rabbit hole. While I don't mind spending money, I like to spend it effectively and not wind up with parts I can't use because I don't necessarily know what I'm looking at, or it turns out one of the parts I need is no longer made, or whatever. All I want is a dang 8 1/4" sure-grip axle under this thing :) And I want to get it on the road this year.

I think the first option I'll go with is checking if the existing axles can be redrilled or not, followed by replacing the axles with ones on a 5 x 4.5" bolt pattern. If I have to swap the rear end, I'll continue to keep an eye out for a 8 1/4" from a 62' to 65', and if I can't find that in a reasonable time period, then a Jeep Liberty or Ford 8.8 rear end. I know those last two are far more available.

I've done hobby auto mechanic work most of my life, but it's always tended to be service and repair things or replacing like for like, not swapping rear ends (of a different type), converting an automatic to manual shift, replacing a front clip, etc. That puts me at the base of the learning curve, and a lot of things you folks with experience already know, I have to learn, sometimes the hard way. While I've always liked Mopars, the '71 Dart and the '67 Barracuda are my first ones, and I lack a lot of Mopar specific knowledge. I definitely appreciate the help and advice.