points refer to the number of elements remaining from the original vehicle. so for example, you change the chassis, you lose 8 points, change the bulkhead you lose another point, change the engine 5 points and so on. when you add them all up, if you exceed the limit, then you have to have an SVA and take a Q plate.
The key to any project like this is to ask DVLA before you start, and you can work out with them what the will require. As an example, they tend to like photographs of the work under way, along with tangiable proof of origin of the bits used. Eg a receipt for the new chassis indicating chassis number, some photos of the new chassis showing the number, some photos of the changeover, some photos of the old chassis being destroyed (i.e. cut up) and finally a receipt from the scrap dealer you give the old chassis to.
Similar for engines and so on.
PLEASE NOTE, the above is only shown as an example and is not intended to be a definitive guide to the points system applied. Each case is individual and down to the owner to deal with. It was merely intended to demonstrate how the points system would work.