Hi S&J
Back in the day they probably just used a light bar.. or ..
simply had red reflectors on the back of the van .. so that when a vehicle came up behind the van at night the driver could see the old darling wobbling up the road....... just before he plowed into the back of it.
or...
Maybe they done as Joe Lucas "the patron saint of darkness" suggested.. get home ( or off the road) before dark
Back to the lights.
No matter what you choose to put on the van there will always be someone who will say thet your choice isnt period correct.
Just put 2 little round red and 2 yellow Narva lights on the light bar or on the van .its enough to comply with todays regs and leave it at that. ... sometimes less is more.
Regards
Reddo