Unfortunately, the Lucas catalogs do not provide much, if anything, in the way of lamp component dimensional information, just the basic lamp size which is typically deciphered from the model number (x575y = 5 3/4", x700y = 7") for headlamps. As far as headlamp door, that is the terminology used in the Lucas catalog for the outer trim ring on headlamp assemblies. Since I started playing around with these things at rather early age and to a large extent grew up in the parts and service departments even before I was born (my mother served as the parts department inventory clerk at her father's dealership early in my parent's marriage). I got used to using the UK terminology in the various parts and service manuals, enough background, back to the issue at hand.
On the 552822, I was surprised to see it was a pinch clamp piece since the pictures of the rally car/rally car replica do not show that. By the same token do we necessarily know with certainty that the lamp assemblies supplied now are the same as what was fitted to the rally car? That might explain the difference. My experience is that most of the headlamp doors were held in place by clips attached to the headlamp backshell/bucket. Having a pinch clamp says to me that there is something on that backshell, a small lip perhaps, that the door grips when the pinch clamp is tightened
The 534343 is for a 5 3/4" lamp assembly so we know that it would fit on the front side but I have no idea of dimensions for the back side of that headlamp door. If you have a line on someone with those in stock, I would suggest calling them up and getting them to check that rear dimension for you. I would also ask if it is held on with screws (some Lucas units did that) or if it looks like it is held in place with clip(s) on the bucket.
Other than that, I am pretty much at a loss for the time being. If I think of something later, I'll either post back or send you private message you ( I assume we can still do that with the new site, haven't tried that yet)