Small to Large Bolt Pattern Conversion

Hello Guys

I am starting to work on and get involved in Moper (1969 Barracuda Convertible).

I have gotten some great advice so far and have more questions. I am assuming my vehicle, which has not been modified (yet) has the small wheel blot pattern. I want to convert to the larger pattern for more wheel/tire choices.

My question is how do I go about this and what is involved?

Thanks