Never heard anyone complain about low gear ratio in a 450SL. The normal complaint is that there isn't enough low end pick-up because of the lack of another gear.
The 722.004 tranny is very similar to the 722.1xx series of trannies and could probably be changed with one for four speeds, BUT that wouldn't help because all MB trannies till the 722.5 are 1/1 final drive ratio; no overdrives. The 722.3xx trannies used in 380 and 500SLs are four speeds but all are one to one final drive ratio.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician