A main dealer fitting a second hand engine sounds strange, if they did I am sure the paper work would record details especially mileage, I think there are quite a few golfs out there about 100k mile mark which have had engine work especially head problems, look at the bills in depth and if it's been done properly it should not be a huge issue, most things are reasonably replaced on the mechanical side. The big issue with the price for me would be the bodywork.. If it has been garaged all it's life and the paintwork is undamaged it would be quite a special car, don't forget though that a car put away when wet and left can rot just as easily as one left outside... Check wheel arches, around windscreen, filler cap from the wheel arch,front and rear valances , bottoms of doors,if they are un molested and clean you could be on a winner if under 4k imo.
