Ian B-B,
Although we can't trace it, the 105 hrs unaccounted for must include an OTU (Twin as you surmise). As I said before, they wouldn't have sent him out to India without one (what would have been the point ?) The time fits very nicely: 25 hrs AFU (to re-accustom him to UK wartime conditions) plus 75 at an OTU.
As for OCTU, that must be anybody's guess. It ranged from none at all (as in my case), where I was effectively "commissioned in the Field", through the home operational squadrons (where it was pretty well the same, but there might have been a quick Course somewhere to teach you how to tie a bow tie and pass the Port to the left (but never heard of such a thing, now I come to think of it). You'd have to ask someone who served the War years in UK.
When you finished our SFTS, you just got your A/PO or a Sgts' stripes (acccording to their taste). In the Arnold Schools in the US, there was this fiction that their Flight School constituted an OCTU in its own right (and all successful US Cadets ended as 2/Lieuts - but that did not apply to us ! - we just got a set of USAAC wings as a Consolation Prize).
But Clewiston was a BFTS, not an Arnold School, so British rules would apply to us (but not the obligatory 20% of US Cadets there, who apparently got the best of both worlds, all ending as 2/Lieuts with both sets of wings !
Confused ? - Join the Club ! Danny.