One of the very few cars I regret not buying was a BMW 750il e32 it had an interior that colour with leather everywhere, even the headlining. I think the interior leather was an £18k option on a 1988 car!
Dont believe everything you read on the internet, that’s not the original car, only one of the 3 still exist and that’s the white Briggs Cunningham car.
From the DVLA website, seems pretty simple to me. Time isn’t based on date of registration but on second time it is taxed.
https://www.gov.uk/vehicle-tax-rate-tables
There’s something in the back of my mind that says the Martini 155s actually had the Volvo/Renault/Peugeot V6 like you got in a Alpine or DeLorean rather than the Busso V6