In part answer to my question, I've read the guidance several times. Chassis change ok so long as it's the direct replacement.
Leaf springs to coil are considered substantial change.
Firstly, I bet you cannot find anywhere that says leaf to coil is not allowed. Just as you won't find anything saying coil to air bag isn't either.
It is all "generic" advice, as there are too many vehicles and modifications to cover off specific examples.
However, to get the logbook changed to Historic vehicle status, you will need to sign to say your vehicle is compliant. There are no tests or examinations of an official nature to determine this.
Historic status means it is "tax exempt", well it won't technically be tax exempt, you will just be in a category that is zero rate, aka £0.00, and each year you will need to "tax" it, re-signing a declaration that the vehicle conforms to Historic status. Again, there are no official tests or inspections to determine this. It is a self declaration.
Then there is MoT exemption, which follows a different criteria. Therefore it is possible to have a car that could be non historic, but MoT exempt and I suppose the vice versa would also be true.
Again there are no tests or inspections to determine if your vehicle is MoT Exempt. It is a 100% self declaration process (assuming the vehicle was built or first registered more than 40 years ago). And when you "tax" it each year, it will do a check and get you to confirm each year that either the vehicle has been MoT'd or that it meets the exemption criteria. Making this also an annual self declaration process too.
However..... because the advice is generic. It allows the DVSA to make their own judgement if they wish to single out a vehicle/owner. And there is probably little you can do should this happen.
Advice:
Vehicle tax exemptions and MOT exemptions for vehicles built or first registered before 1984.
www.gov.uk
It is all very clear and easy to follow.
The "points" system people refer to is very much a red herring. As there are multiple systems:
How to register your vehicle and the cost - new registrations, kit cars, rebuilds, radically altered vehicles, old and classic vehicles, vehicle identification numbers, Q plates
www.gov.uk
How to register your vehicle and the cost - new registrations, kit cars, rebuilds, radically altered vehicles, old and classic vehicles, vehicle identification numbers, Q plates
www.gov.uk
CLICK both of these, they are different links...
Note there is no system or test to determine which set of guidance applies, this is also a self choice. They are similar, but not identical and one doesn't use points at all. Also these are about "registration" and if the vehicle is eligible to retain its registration. This can have the knock on effect that a registration change may then not be eligible for 'historic status', aka Tax exemption. But said vehicle could still qualify for MoT exemption if it meets that criteria. But it is all pretty easy to follow.
Ultimately, nobodies "opinion" matters on what is or isn't allowed. You have to read the guidance yourself and then personally decide if your vehicle conforms or not and if you believe it does, sign to say it does, aka self declaration of YOU taking responsibility for the decision.
For example, if you look at the either the radically altered or rebuilt vehicle regs they say this:
A rebuilt vehicle can keep its original registration number if you can prove you’ve used:
- the original unmodified chassis or bodyshell
points must come from having the original or new and unmodified chassis
Chassis, monocoque bodyshell (body and chassis as one unit) or frame - original or new and unmodified (direct from manufacturer)
What is not offered is any definition of the word "modified".
Drilling a hole, bolting on a bracket or welding something (even a repair patch) could quite easily be deemed a modification. Therefore fitting of rollcages or different engine mounts may be used as an argument. Yet plenty of cars with such modifications exist. So this is where the advice is grey, thus giving the DVSA the power to single out individual vehicles if they so wish.
Another example:
What is meant by "steering assembly"? No definition is offered or given. Is a steering wheel part of the assembly? Technically I'd say yes it is. But it would seem very harsh that an aftermarket steering wheel would lose you 2 points on the Radically Altered Vehicle regs.
So it comes back to you as an individual to decide if your vehicle meets the guidance and if you can justify how and why.