Just a heads up on this. I have had a couple of calls on this. Like anything, its possible to do. Beware that there are a couple of differences in the system that may or may not have been overlooked.
1) The center distance between engine output shaft and transmission input shaft are different. So the BDM inner primaries are proprietary to the BDM bikes.
2) A RSD transmission has standard H-D primary to transmission mounting holes. Where as the BDM has a Proprietary set up.
3) The BDM proprietary transmission mainshaft length is a lot shorter than a regular RSD. If you look at any other RSD bike you will notice a gap in between the primary and transmission where the left side drive belt would be. Hence the Slam Clutch.
4) Another thing to look at (which some of you mentioned), is the rotated down and to the rear starter location. This will cause oil tank issues for sure. On rigid bikes, you can just fab up a tank for underneath the transmission. Rolling Thunder does this on some of their frames.
Just a couple of my thoughts. Pretty interesting thread. Keep it up guys!!
Let me know if you have any questions. I will try and follow this.
-Scott