Mine are 215/70/R15 Firestone FR710's with a 7/8" whitewall. It's almost impossible to find wider than a 7/8" now, even at the specialty places.
The first number, eg 215 or 225 is the tire width in centimeters and the second is the tire height as a percentage of the width. Headacheguy's tires are wider, so slightly higher, which means overall a bit bigger. That means that with the 215's you will be traveling a bit slower than with the 225's at the same rpm (less than 2%).
However, since the cars originally came with 8.15 x 15 bias, it's pretty hard to say which is best. By the way, the difference between the height of a 215 and a 225 is about 1/2", with the 225 closer to the original diameter, but the 215 closer to the original width.
Hope this helps (although I don't see how it can).
Terry
64HT