stock 67 barracuda rim size?

Your car most likely came with 14x4 1/2" rims, although disc brake and Formula S cars would've had 14x5 1/2" rims! Originally, your car would've had the 5x4" bolt circle, but it sounds like the change was made to the much more common 5x4.5" bolt circle, which is a good thing! They are better brakes, and a much wider rim selection is available!

There will be no problem running large bolt on the front and small bolt on the back, you would just have to keep two spares in the trunk, one for each bolt pattern! It will also not be a problem changing the rear to large bolt, depending on what rear end you have! If it is an 8 3/4", a simple change to the aftermarket large bolt axles and corresponding brakes will solve your problem! No need to switch to disc in the rear, although it is very doable!!!