How hard/expensive is it to switch out gearing on an A-body?

UPDATE - they are Moser A-body axles with large bolt pattern (I dug out the receipt from when I purchased them 10 years ago). When I went to install them they wouldn't go in the last 1/4" or so, wound up pulling the center section to take out the spacer buttons.
Refresh My memory real quick, what is the diff in length between R & L 8.75 axle shafts?