As Ed said, the center hole on your wheels won't fit over the hub on a modern axle without turning your wheels on a big lathe. I had this done on a set of late '40s lock ring rims year's ago so they would fit on a late 50's axle...the hole went from 4.75" to 5.25".
Also bear in mind that by just change the rear to modern faster gears doesn't mean your actually going to be able to go faster...your engine won't have enough torque or HP to turn the faster gears unless you're going down hill. The factory spent a lot of time working everything out so the engine, trans, rear and tires would all play nice together. If you change one of these items it will effect performance in a negative way.
Mike B
