Remember
The AC MKIV frames needed to be beefed up for 1980's DOT, therefore a derivation from MKIII chassis. They are stiffer for sure!
All special orders were taken off the line, therefore they tend to be blends of MKIV and MKIII
Alloy bodies also varied as front snout (for DOT pass) and door angle all were variable in these cars.
The doors in some of these cars still carried the crash beam necessary for importation and other did not.
Certain cars, Trevor Legates, were MKIII exacting but that is the exception.
I have this discussion alot with folks that have special order cars.
As a Friend told me, Brian did anything you wanted as long as you paid. $
