Facts are,
There are a possible total of 14 points for tax exemption. You have to retain 8 points to continue claiming tax exemption (Historic Status).
1 Point for the engine.
5 Points for the chassis.
2 Points for the transmission.
2 Points for the steering assembly.
2 Points for the suspension
2 Points for the axles.
= 14 Points in total.
For example, if you change the engine for a newer type 2.5 you will lose that 1 point. If you change the gearbox as well (for a newer type) you will lose another 2 points and so on.
Digressing slightly it's all designed to catch you out on the coil conversion with a cut down RR chassis. Lose the original chassis and use a cut down RR chassis with the RR coils and you've lost 7 points, therefore you can't retain 8 points. I know this much to my cost.
A RR chassis must remain at 100" wheelbase and be before 1973 to retain it's tax exemption because it is still essentially the same vehicle as on the V5 document. It doesnt matter if it has a telephone kiosk as the body, it's still an unmolested chassis.
Anything thats been cut down to reduce the wheelbase must be SVA'd as the structural integrity of the chassis has been altered. Believe me the authorities are clamping down on rogue vehicles that have been reduced between the wheelbase and which carry a tax exempt VIN and V5.
On a lighter note, series Landys are much more workable with replacement parts, if you put in a replacement reconditioned series engine this won't affect any points. The same goes for Parabolic springs, they are classed as a "Direct replacement part" so therefore the points system will not be affected for any vehicle before 1973.
Regards WP.