4" to 4.5" Bolt Pattern on a 7 1/4" Rear?

I just read the thread and saw the pic in your last post. Are you sure which axle you have? a 340 should have 8.75. If so, then axle shaft swap is easy. I got my BBP axles from Moser Engineering fo my swap. http://www.moserengineering.com/ .
They have several perf levels , I got their street axles. They probably have a set ready to ship.