16's on a 65 Barracuda?

As long as you stay with same overall tire diameter and the correct backspacing and width to fit in the wheel wells you can use any wheel Diameter you want! :D

My car has 17X7"s off a 06 Charger with 225/45-17 tires in the rears which are same overall diameter as a 205/75-14 (stock size) tire with room for even a wider tire maybe a 245?

I'm using 1/2" spacers with longer studs and if I remember right the overall offset is 4.75" front and rear (I think 4.5" would be ideal).

If you go with a 16" or larger tire size you'll have a whole lot more choices in tires as well, and the they wouldn't cost you much more then the eqivatent 13 or 14" tires!