It would be cheaper to rent a car. The combined work of removing and replacing the trans twice is equivalent to the work needed to do the appropriate repair once in the first place.
The 722.3 and .4 trannies are very similar but they might have a slightly different length which could cause problems. I'm thinking that the 260e had the .4 tranny in the same body as the 300e had a .3 tranny. If thats the case they might just work.
Bosch Master, ASE Master, L1
33 years MB technician