Philip, what exactly are you looking for for thge class 66's, which versions, in the uk there 5 different versions...
there's, 66/0/1/2/4/5/7 which are effectively the same locos although there are earlier and later versions of 5 & 7's, which are diffrenciated by the large or small headlights, the larger ones are later locos to meet the later Railway Group Standards (GM/RT 2180 issue 3)
66/5 again early and later versions these are lower geared but no external differences from 66/5's
66/951/2 which are low emmission locos, to meet the new UIC 2 regs, the UIC 3 regs are on the way so later batches will be slightly different again.
UIC 2 locos have extra engine room external doors (similar to the cab doors), smaller fuel tanks, and enlarged cooler groups.
The european locos differ fro the Uk ones to meet the requirements of the UIC, so have different lighting on the front, different lamp brackets, brakes comply to the UIC (different brake timings on application and release to the UK), plus signalling systems for the respective counties they are working in, cab layout different on some.
The Scandiavion locos also have extra cold climate equipment, double glazed side windows (similar side windows are also fitted to the UK 951 and 952 locos).
Locos UK operators are:
66 0/1/2 EWS
66 /4 DRS
66 5/6 951/951 Freightliner
66/7 GBrf
I hope this is of help.
Regards
Ringo