Overdrive tranny in an A-body

Hello,
I am considering installing an A-500/518 overdrive transmission in my '73 Duster which will be getting a 5.2L Magnum soon.

Has anyone out there performed this swap ('70-'76 A-body)? How much floorpan modification is involved? Is this even doable?

This would replace the current 6cyl A904.

Any help would be appreciated.