Hi Tracy
Good timing! I had prepared some suggestions for your continuing research.
His service up to May 1943 was all in the UK and his initial time in the holding battalion is not worth looking at. There is no war diary for 19 or 10 Battalions - unsurprising, they were based in UK. What they were doing and where you would find out I suggest at the museum:
https://royalwelsh.org.uk/ The museum don't have info on individual soldiers.
I suggest you concentrate on the Royal Engineers from 1943 onwards when he is in the same unit throughout and with which he served overseas.
This link
http://www.rootschat.com/links/01ot5/ is to the History of the Royal Engineers from the year dot. I'd suggest Volume 9 is what you want specifically.
The link also has links to the RE in-house Journals.
With these it will be a question of checking out the contents of the history and journals for mention of the Inland Water Transport units and with fingers crossed for 980 IWT Workshop Company Royal Engineers. Be aware though that the IWT were one of the lesser known elements of the RE so it may well not appear at all! Nonetheless anything on the RE in Burma/India/Singapore late 1945 on will be good background. The history does mention post war Japan, page 578 onwards - the bit about allied supervision of Japanese contractors would fit my theory that he went as a senior advisor to one or other of the units that were there.. There are I think too many RE units there to try to find mention of one individual for just one month in 1947!
It would be good if you can visit the National Archives at Kew. There are 5 war diaries entitled 980 Company RE from May 1943 to Dec 1946 which almost completely cover his service with them Although the word "workshop" doesn't appear in the title, I don't find any other 980 Companies and the places coincide with his dates (UK up till Mar 1945 then Far East until Dec 46 (doesn't quite go far enough!). There is nothing beyond Jan 1947 when he went to Japan.
There is also a war diary for 52 Indian General Hospital
https://discovery.nationalarchives.gov.uk/details/r/C2738517- it won't have his personal records but it should say where it was while he was there,
There is a lot there, check out the links and shout if you need more now or when you are back at uni again - don't forget to study your uni subject(s) though, the military side can become addictive!
MaxD