Looking at those regs I can see nothing about conversions other than a stroker kit maybe or running on anything other than petrol for very late models! Most of those rules have always existed
'Changes you need to update.You’ll need to tell the Driver and Vehicle Licensing Agency (DVLA) about the following changes to your vehicle:
* colour
* engine
* cylinder capacity
* fuel type (propulsion)
* replacing or modifying the chassis/monocoque bodyshell
* seating capacity
* weight of a goods vehicle
Change to engine and cylinder capacity (engine size)
DVLA will need written evidence of any changes to engine number and cylinder capacity (cc). Written evidence can be:
* a receipt for the replacement engine
* written evidence from the manufacturer
* an inspection report provided for insurance purposes
* written confirmation on headed paper from a garage if the change in engine size took place before you bought the vehicle
Change to fuel type
DVLA will need written confirmation of changes to fuel type for vehicles registered after 1 March 2001 if:
* your existing engine is converted, the confirmation must be on headed paper from the garage that carried out the work
* a new engine is fitted, the receipt will be required as confirmation'