It's been 25 years from when I last sent a motor for inspection.
This is done on a points scale.
Chassis
Axles
Gear box
Engine
Body work
All these have different values. You have to list these to and get above a score to keep your reg/age of build.
A file of receipts for a build helps so do photos.
This was a series 2 where I converted the existing chassis to take coils. Yes I left the spring hangers on incase I had problems in the future of the age of the chassis.
Just about retained ref/aged plate.
And yes it had an engineers report.
@nobber how long have you had the motor for and have you always had this mot/taxed?