What rim size can I run?

So it looks like my front rims are part number 3580055 which states 14x5.5

I acquired a set of 15 inch rims from my friend who had them on his 75 duster. They fit the car good and look to clear the leafs and wheel wells. I may not go with the same size tire that is on them but these are a good start.

Tomorrow I plan to hit the JY and see if I can find 2 for the front. If mine are currently 14x5.5 Should I look for 15x6 or 15x6.5's?

Here are some of the pictures of the 15 in rim on the rear of my 73 Valiant.
159757215_498324067837427_3822537841232384235_n.jpg 161574064_191233176135761_35111012129893683_n.jpg 160562056_728133341209574_1052918079308592835_n.jpg 160568798_189360682686936_9131350606102163314_n.jpg