The points system has been in use since the 70's, VOSA just kept it quiet
To keep your original registration you must total 8 points or more. All the details are in the links provided by frodscrote.
This, at the moment, will only be a problem for you if your car isn't on the DVLA computer and you need to register it. That would most probably involve it being inspected to confirm its status, as would a cherished transfer etc. If it was chopped about and a mix of parts its game over really, unless you fancy trying to get it through the new style SVA (BIVA?)
But, you said you had declared SORN so you must be on the DVLA system. You only need an MOT and insurance then you can tax it. At this point in time you won't have a problem with the MOT man but there has been rumours that there's plans, in the future, for a tick box on the MOT form to state the vehicle is modified. At that point in time you may be in trouble.
My advice, don't modify the shell