It seems sensible that '700' refers to 7" units and '576' is a 5¾"
I would like to (eventually) fit driving lights as well, and I'm torn between a pair of period correct 576's and a pair of Cibie Oscars that I've used on most of my cars since around '75
,
so while not quite period correct, the Oscars have 'history' and have survived remarkable well.
Cheers,
Glen