If you want to yield a stock Mopar pinion offset, make the drivers side tube (and axle) 1 3/8" longer than the passenger's side.

If you are using equal length axles, both tubes should also be equal length.

Keep in mind, the axle end gap is 1.75" for Dana rearends and 1.5" for 8 3/4" rears. In other words, if you want to build a Dana around 8 3/4" axles, you need to make the Dana housing 1/4" wider than the 8 3/4" donor housing.