There was a change in the rim lip contour, I believe it was a bit earlier than '55, though. Has more to do with the change from tube type to tubeless tires, with the taller lip on the tubeless rims acting to "lock" the bead of the tire to the wheel. However, if you ever get a chance to look at a 14.5, 15.5, or 16.5 wheel (the first 2 are trailer wheels, BTW), they have virtually no lip at all, even with tubeless tires. I've mounted tubeless tires on the earlier wheels without any problems, as long as the inflation isn't let to get too low.
As far as the whole "bias ply wheel vs radial wheel" thing, I've been told that the radial wheels are supposedly thicker in the web area, and are able to handle the increased side loads that a radial tire can handle. I'm skeptical about that, steel wheels on todays cars tend to be pretty thin, very easily bent with very little force. Unless you're planning on doing some high G road course racing, I don't see any problem putting radials on older wheels that are in good condition.
