As for the 4 wheel drive isue why not ask any one of the numerous SL-C owners with Gaziano's (something about trimming block to clear out shaft but don't quote me on it. It's been discussed here before)in them as they seem to have that pretty much buttoned up at this point.
Do you have any links you could post? My searches are not turning up much.
Along the same lines, has anyone done this with a 6HP26A? Looks like these transaxles are reasonably inexpensive and are rated to 400 ft-lb+. Also lighter than the 5HP series, from what I understand.