Wheel Question

My '70 Coupe came with F70-14 tires and standard steel wheels. I needed to remove the tires to have the bead resealed because after sitting for 13 years at least one had a slow leak. While the tires were off, I decided to have the rusty wheels blasted and I would repaint them. This was done.

In preparation for painting, I had all of the wheels sitting together and noticed that one was different. I already knew the spare was not as wide, but of the four mounted on the car one was less wide than the other three but still wider than the spare.

I am not sure where the wheel dimensions are determined. If I measure the O.D. (outside diameter) from lip to lip it is about 15 3/8". If I measure the first internal flat area inside of the wheel lip, I get 14". This corresponds to the tire designation, and I assume this is correct. Please confirm or tell me the correct way to measure!

Using the approach to check the width, for the widest wheel the lip to lip dimension is 8". If I use a similiar approach for the width as I did for the diameter, then the widest wheel would instead be 7".

Presuming my method is correct, I have of the four wheels that were mounted on the car with the F70-14 tires three (3) wheels that are 7" wide and one (1) wheel that is 6" wide. The spare wheel which does not yet have a tire is different still. It is 14" diameter, but is thinner still at 5" wide.

Having the spare different doesn't bother me, but I wonder about the wisdom of running different size wheeels even though they would have the same size tires. What is the collective wisdom?

If I need to change, should I get another 7" to replace the oddball 6". Or should I get another 6" and run those on the front, with the 7" wheels on the back? Does it matter?

I have seen many adds for the dress-up wheels, but where does one find just ordinary stock steel wheels? Is this a salvage yard only item?

Thanks for taking the time!