In late 72 and all 73 the mounting brackets in the front bumper were modified
by being Boxed rather than an open sheet metal bracket...and the location
changed "as much as" 1/2 inch according to the Leyland service bulletin. Also
tho...the alignment of bumper bracket, frame tweek and
hole-in-valance-to-bolt-shank will allow about 1/2 to 3/4 inch up and down
alignment in a car with a straight frame anyway. So arguable as to whether
the boxed bumper brackets actually were lower or just got assembled that way.
My 70 TR6 has a fair gap between the lens and bumper...larger than Dan
Green's 73 (club member and original owner). So probably no true correlation
leaving the true design variants at "three" as suggested.
Bill Burroughs, So West VTR National Rep, 70 TR6, 68 TR250, 59 TR3A,
73 MKIV, 69 GT6+ and two 65 TR4A Vintage Race cars. Happy Motoring!