Hello
I'm also researching the Class 66 at the moment and see there appear to be three types based on the type of engine they received.
12N 710 G3B-EC for UIC I
12N 710 G3B-U2 for UIC II
12N 710 G3B-T2 for Stage IIIA
Platform 5 (British Rail Locomotives and Rolling Stock) only lists them as...