axle width of an FB?
 

any have a tape measure and what to get the width, hub to hub of an rx7 axle?

I just measured a rear end I have laying around and its 57 inches from the hub face to hub face. I measured the distance from the outside edges of each brake backing plate, 54 inches. Then I measured the distance from the outside edge of the backing plate to the edge of axle flange, 1.5 inches. So 54 + (2*1.5) = 57 inches. This is an SA rearend but should be the same for 81-83 FB axles for sure. Not sure if the GSL or SE axles are any different.

interesting that means i could probably run the 59.5 inch wide mustang 8.8 without modification to the axles. Just fiddle with the offset of the wheels if needs be.

The SE axles are a bit longer. SE rearend is closer to the same width as the mustang 8.8, so using it you would need wheels with the same offset that are typically used on SE's. Around +35 to +45, depending on wheel width.

the 8.8 solid rear is only a half inch longer than the stock 1st gen rears on each side (making it one inch longer in total). wich is plenty fine to just put it right in there. and they now have gears all the way up to 6.14 for it since it's getting more popular to use.