This topic has bugged me, so I looked into it some more. There appears to be some information out there that would suggest some of the features of the Hiwatt I pointed out as signs of forgery are "correct" for the DR105, which was a Canadian-export only model. The trouble is those sources also conflict with each other and this amp on a few key points. First, it is claimed that no voltage selector was used as Canadian electrical regulations would not allow for voltage selection, which is certainly not true today or otherwise modern switching power supplies would likewise be illegal there and I seriously doubt such regulation existed in the 70's either. Some "had" a hardwired power cable and supposedly required transformer bell covers and IEC sockets for power cables. The trouble with those ideas is this (as I pointed out earlier) is that the IEC socket standard did not exist in 1977 and that Partridge has NEVER made transformers that had bell covers, even on much larger and more potentially lethal applications.
I want birdie to know that I have never doubted his sincerity or honesty for a single moment, but I still have serious reservations about agreeing with him that his amp is in fact a stock 70's Hiwatt. I would also like to point out that there is a business in the UK that is notorious for faking vintage Hiwatts and Marshalls and then using online forums to try and legitimize the different "feature set" when compared with an inarguably genuine vintage Hiwatt by spreading disinformation about "model variations." The amp in question probably sounds exactly like a vintage Hiwatt if the parts are close to spec, but I simply cannot endorse it as being a 70's Hiwatt. Of course I could be wrong, so take any advice I give with a grain of salt and weigh it with your own discretion.