It has been a long time since I did it, but the main issue is the input bearing size. On the OD case they increased the size of the front bearing, mainly because power in OD is always going through the cluster shaft. In a regular 4 speed they lock the input shaft to the output shaft for 4th gear so the gears are just turning in the oil, no power going through them, main reason they last so good. So if they are putting the OD gears and using the small bearing diameter, in a Hemi trans, not sure how it would hold up. Used too be a lot of the dodge truck OD transmissions 23 spline were available in junk yards so we had the hole in the bell housing machined to fit the bigger OD bearing housing and it was a bolt in deal pretty much. Any decent machinist can bore the bellhousings. So if you are using the Hemi spline then one of their kits might be the way to go. But I would defiantly ask them about how the input bearing holds up, Chrysler engineers made it bigger for a reason in the OD units.