the original question still remains unanswered. should an f-plate mk2 have big bumpers from the factory?
For me, no, It should have small bumpers if it's a genuine UK spec car and not an import!
BB cars would have undoubtably been available in Europe before they made it to the UK, but at what point in time, I do not know.
Many GTI's found their way over to the UK via the British Forces during the 80's and could easily be spotted over here because they still ran the German registration plates, which was soon sorted after fear of the likes of the IRA targeting cars!
So for a definite answer, the OP would have to contact VW, and pay for a Heritage Certificate, or do some homework on decoding the build sheet if he has it!
Thom