At the moment, with the way legislation is potentially headed over here, anyone that is seriously contemplating major mods on a vehicle like this really needs to do their homework before committing. Even if you transplanted the entire chassis/suspension/ steering and drivetrain from a single donor, which in the past could have been passed off as the original 1990s Defender/Discovery/Rangerover with a rebody, at the moment it looks like it could still be considered a significant change, so triggering a set of test criteria that getting a 1950s body through would be challenging.
I'd love it though, if I didn't already have too many things to do.
It's probably worth seeing how it settles, but I've been reading a lot about the legislation changes, and so far I haven't seen anything to stop the re-body approach. The changes look to mainly focus on how to define which vehicles are MOT exempt, but this will of course catch those cars that didn't follow the rules.
Exactly the reason I'm looking to follow the rules!!.
That said, as noted above, "Custard" was meant to be a relaxing between jobs build and instead is actually surplus to requirements. I do love it though, so am not rushing to sell.