Hi Julian,
the green diesels are there, so as far as I am concerned, the period is mid - late 60s, but having seen a clip on YouTube taken at Crewe within the last month, there was nearly every livery that has even been on British metals. So many of the older generation of diesels are now being restored for Mail line use, anything goes seems to be the order of the day!
I fancy following the numbering/livery history of Brush D1643 as the latest Heljan version would allow that which would produce four models up to the late 90s, even more now that it has been restored.
I think that all green livery would become a tad boring and at the end of the day RULE 1 always applies!
Just applied the first coat of concrete onto the slabs and will let that go off until Monday - it is our Open Day tomorrow, thankfully we shall not be directly in the sun for too long.
regards
Mike