Rear End Questions...

You don't need to move the perches, you can press the springs out eh 1/2" per side.

The best and correct way is to move the perches in 1/2" per side.

One downside to the B rear, it is wider so you need rims with more offset to get the tire back in your wheelwells. It's a popular swap. 65-67 B's are the best choice then the 68-70 B rears.

If you do the B swap, use a plumbob to get the axle centered up in the wells. You can also set pinion angle while you are at it. The cars usually aren't perfect to either side. My Duster has 3/8" bigger rear wells on the pass side than drivers.