I think it's still owned by Neil Murray, who was registrar of the Aston Martin register at one time, and is raced by his son I think. If you needed to find it or them the Aston Owners Club should be able to link you up.
Not sure what it's current state is, but when he first bought it the tail had been shortened by about 18", though I think he has had it rebuilt, so some of your reference photos may appear to be giving you conflicting sizes.
Not experienced in these things yet, but from my deliberations of trying to get all the bits to fit, there does seem a suitably sized bit of room between the seat and the rear axle, something I'm fighting with at the moment! After that it all starts to get a bit difficult with the tapering of the tail. - Looking forward to the build.
Peter