To go slightly off topic, if I may, on the 1969 Circuit of Ireland I was co-driving the very quick Jock Russell in a 911 Porsche with a Stuttgart 'works' 2.0 litre engine. Unfortunately the suspension broke and we couldn't fix it in the 15 minutes max lateness allowed at the start of each special stage. So we went to help our good friend Rob Lawrence who was in his newly-acquired ex-works 'S'.
He was lying well into the top 10, but the car was getting very hot. I noticed that it had been incorrectly with a 16-blade fan so we needed to change it for a 4-blade which we didn't have. Rob's mechanics asked the 'works' service crew if they could let them have a 4-blade fan, but they said no. So I went and found Paddy, who sort-of owed me a favour, and he went and got me a 4-blade fan straight away. We set up for changing it when we had about 45 minutes available service time and we got there a bit early and set up to do it. I said I would do it, but that I needed to be passed the tools when I asked for them. We did it in about 35 minutes and Rob went on to a top 10 finish, which pleased the 'works' team as they had 3 Minis in the top 10 on a major event.
Rob did a lot of rallying in that car and it must have been very tired by about 1972. I would assume it had to have another shell, but back then we would still have regarded it as the same car (I still would!) as that was what happened, and still does.
The problem with this car now is the availability of continuous history, not a shell change. Now that is where the big question comes!
What used to happen, shell-wise, was this. A rally (or race) car would have a shell which was no longer fit for purpose due to accident damage or simple wear and tear. There were a lot of 850 Minis which were involved in accidents and the cost of repairing them was deemed not economical by the insurance companies. However, the damage was not bad and they were otherwise rust & damage free. They would be bought for salvage and a shell with minimal damage when stripped down could be bought for maybe around £75. Whilst stripped it would be repaired, an easy job, and seam welded and strengthened as necessary and the old car simply built into this shell. It might be painted the original colour, or not. It was not a long job with several people working on it and the car could be rallying in around 5 to 6 weeks. This was all accepted practice and if 850 shells were as readily available now it still would be.
Of course, the purists, who in the main were not competing at that level in the 1960's & '70's, will be aghast at this, but it was necessary. If I badly damaged my 1964 Cooper 'S' now I would still do it rather than lose the car completely.
Yesterday I was with a guy who is a senior person in the classic car movement. There was a meeting with the DVLA not long ago and the subject of re-shelling came up. It seems the DVLA stated the rules, but then said that they are not really interested so long as the car is correct in its model/type specification and has the correct VIN and engine numbers and is properly MoT'd and insured. They are only concerned if there is strong evidence the shell is stolen and they need that before they will even start to investigate. So it is not really the big issue some make it out to be. After all, the body-shell was just a part number in the BMC parts lists.