Simon,
It's great news that more 40's are going thru SVA, proving it's not impossible & getting more 40's on the road.
Have you considered that you can skip the necessity for an SVA by buying a car already registered & re-building it to your own spec?
It's by far the most cost-effective way into building, owning & driving a 40. Current s/h values are low, especially when compared to the cost of building a car from scratch.
When I was doing my sums prior to ownership, I found you can buy a basic spec used GTD (302, renault 'box, leather, air-con, etc) for about the same price as a new rolling chassis. It's a long & expensive road from a rolling chassis to a complete car!