The SOU and 2/3(5?)/52 tells me that it went through a full Base Workshop overhaul at 18 Base (South West Command) Workshop at Bovington in Dorset and was out-inspected on that date. I'm not sure that I'd agree with Brian (thread 2) that the 46 indicates a factory repair date. If it did, it'd be marked as a factory repair date. There, a little bit of history for you.