M-body 8.25 posi to a 66 A-body questions

Hersbird said
That sounds closer to the a body axle, I thought you were saying it was 1.5 inches per side wider. Although you might want to measure the wheel mounting surface to mounting surface because if you are using the brakes from the cop car there might be a little more spacing there as well. This thread seems to say 15x7" with 4.25BS leaves 1" clearance, so a 5" might fit pretty well. If you go over a bit with backspacing you can get if back with a spacer while to little back space will take away some of your room on the outside. http://www.forabodiesonly.com/mopar/showthread.php?t=186503

On the driveshaft that should be right but you might want to get it all together and measure it first to check. Are the u-joints the same size?

You as stated you need to measure outside drum to drum. The newer cars have wider drums and that seems to make a difference when upgrading an a body 8 3/4 to large bolt pattern by requiring longer axles than original. Some of the backing plates and drums are comming off the M body rearend you are talking about.

It is very important that you get the perches in the right spot on the tube because if they are too far forward or backward it throws everything out of sink resulting in vibrations from hell.