Latest update:
Received the revised oil cooler from TPUK along with the updated longer hose required (ordered together). After a slight hiccup with missed messages they also were kind enough to supply the necessary longer bolts for free too (and threw in a new sump plug I'd enquired about buying as well to make up for the hiccup!).
There is a clear difference between this part and the other one I purchased from another seller on ebay initially. The TPUK part has a much neater, higher quality casting, holes are drilled more precisely and the interface between the oil cooler radiator and the oil filter mount appears to be manufactured to more precise tolerances.
The oil filter and oil filter mount both have part numbers and manufacturer's stamps, however they have both had the manufacturer's name ground off. As Jim said, I'd also wager a lot of money they came off the same production line as the genuine branded parts.
For anyone else reading this and looking at fitting this updated oil cooler - my earlier estimation of the required bolt sizes turned out to be correct. Five x 35mm and one x 75mm, all M8.