722.3 transmissions were fitted to W123 W126 and R/C107 chassis you might find them fitted to other vehicles as factory standard as well but they were mostly about in the early 1980s although they were still used in some vehicles made later I believe.
If you look at the EPC catalogues on
EverythingBenz - Mercedes-Benz Forum and Web Search Using Google you can find out the transmission numbers you might want - but it is best to speak to people who have done this before.
The "diesel" valve bodies for example will probably shift too soon - though you can probably adjust the shift points with superior shift kits it is probably best getting what people advise rather than trying to turn apples into pears (so to speak).
The majority of the 722.3 transmissions share the same gearing - only the valve bodies changed. Towards the middle of the 1980s with the introduction of the 722.4 transmissions the quality of the parts in the 722.3s seemed to tail off too - it all started to go plastic.
If I remember correctly the "V8" 722.3s had different gear ratios - but I'm not 100% sure about that. If you want to know about specific transmissions I can probably find out information for you but I'm not willing to write out huge great big lumps of information at the moment (got no time!).
The myth that diesel transmissions are stronger than petrol transmissions isn't true
Look out for electronic and mechanical speedometer compatibility related problems!