Well put Paul, but the most important part is the "ORIGINAL UNMOLESTED CHASSIS"
You will only retain the registration if the "ORIGINAL UNMOLESTED CHASSIS", scoring 5 points, and 2 major components which will score at least 3 points.
This makes a total of at least 8 points, meaning more than 50% of the original car/components where used.
VOSA say a car is made up of 5 major components each have a points value.
Chassis = 5,
Axles = 2,
Suspension = 2,
Steering = 2,
Transmission = 2,
Engine = 1,
Total = 14.
You must score at least 8 points (5 of which must be the chassis), or use over half of the original car to retain the registration.
When a Sammio is built we actually score the full 14 points.
The only problem is the rear out riggers on the Herald and the bonnet mounts on the Spitfire. When these are "removed" it could be classed as a modified chassis
Note, VOSA do not include the body work as a component and this is why no IVA is required.
When dealing with DVLA another golden rule is "if they don't ask don't tell them", and of course "kept it simple".