It's only slightly more involved, but you can get different input bearing retainers that will fit to limit the need for adapters. I had a non O/D 4 speed in an O/D housing that used a factory input retainer. It's a fairly rare piece though and fetches a slight premium over the more plentiful sizes. I got mine from Wildcat salvage in the Northwest (Washington or Oregon I think). Wasn't too expensive either, I think $50-70 if I remember right.
