I presume when you mention FA-2 you're ruling out the early 'teething troubles' with the engines, like the original cast cranks that didn't hold up and that apparently caused damage requiring engine replacement, and the original GE turbos that worked fine at 30,000 feet but not so well in a carbody. The water-cooled Alco-designed replacement worked somewhat better, but UP said in 1953 they were not ordering new Alco road power because even the revised turbo was causing manifold failures in heavy fast road service in many UP locations in the West.
Union Pacific did not have that mant Alco road locomotives. The big purchase was 88 FA-1 and FB-1 units, with 11 RSC-2 units for branch lines and 5 RS-2s, also used on branch lines. Cynthis Priest in The UP Diesel Volume 1 indicates that UP chose not to replace the air cooled turbochargers in the FA/FB units. She seems to know something about the 244 from her description. there are photos of RSC-2s in the late 1960s showing the distinctive offset stack associated with the air cooled turbocharger and also on one RS-2 in 1959. Other units of both types did show the transverse water cooled turbo stacxk around the same time. So perhapps UP were referring to a modified air-cooled turbocharger.
It is suggested that UP spent some time tuning the 244s to overcome the problems and it is possible that even a 244 with an air cooled turbo could be made to work, at least until the 1960s.
I'm not sure when the water cooled turbo actually became available as a retrofit. The earliest new unit fitted with a water cooled turbo that I have found is a 1955 SP RSD-5, but the units before that one were purchased in 1953.
To my own experience, during the 1954 Royal Tour of Australia in February and March 1954, the NSW Railways ran two RSC-3s painted Garter Blue on the Royal Train, and photos show that these still had air-cooled turbochargers. I would suggest that if the retrofiit had been available by the end of 1953, those units would have been fitted.
This visit is covered by
The Queen In Australia (1954) | NFSA
The RSC-3s appear (briefly) at 45:54 and the other well known train, that of the VR with the double ended EMD ML-2s gets much better coverage at 49:40.
This is an amazing film. Not only is the view oof the Queen in the Daimler in George Street Sydney exactly the view I recall, from the roof of my father's office building, but the scenes of Canberra where I now live are clearly recognisable although there are large areas of grass where there is now a lake, many buildings and many additional roads. It is hard to believe that things were so different then, even though I was there. Just before the RSC-3s here is a scene with a QANTAS Super Constellation, and there are many other scenes for car and aircraft and ship enthusiasts.
But to get back briefly to the subject, I don't think the water cooled turbo was available as early as 1953.
Peter