"Peter Lawrence" wrote

Which coaches were short enough that 4 of them would fit in here -
class 501 perhaps??

Weren't 501s 3-car sets? After them, there was a period when 2EPBs were
used, but AFAIK they were only used as 2-car trains on the NLL. 6-car 501s
were used on the Broad Street - Watford Junction route, but they used
Willesden Junction New, not HL.

Peter