How are you getting on with this?
I saw a picture of a 722.3 automatic gearbox for a 500SEC the other day whilst browsing through some classifieds and I saw that that gearbox had two starter motor "ears" on the casing. One on either side. Sorry I can't find the picture now of course - but if you look here on this advert for a 300 SE / SEL you can see a 722.3 with a starter motor ear on the left hand side - rather than the 722.303 (for a diesel engine) which has the ear on the right hand side:-
http://link.marktplaats.nl/463652783
It looks like it is more complicated than I thought. I still think if you can find the chassis numbers you'll get a better idea from the list of gearboxes posted by rs899 in the link I posted above.