Rear end

I have a '70 Chevelle with a factory 10 bolt that I need to replace the rear end in. I have a 12 bolt from a '69 Chevelle but the control arm brackets and shock mounts have been changed. I would like to use the ones from the 10 bolt, but don't know how to get the alignment right as far as the correct placement in relationship to the drive shaft ( rotation). I can measure side to side to get that right. I can remove them from the 10 bolt and weld them on the 12 bolt myself if I can figure this out