Hi JM. Hi to all.
I'm new here, but have been making curries on and off for a number of years. My answer to your question and my opinion on the 70's and early 80's madras would have to be "simplicity". The establishments back then, were, from recollection, basic to say the least, as were the curries they produced. Some of the best curries came from scruffiest joints around.
Most were run by someone from the local community who was not necessarily a chef, just someone who could cook. Someone who was out just to make a living so to speak. I wouldn't have thought they went overboard with too many ingredients. Probably just a simple straightforward onion base along with a minimum of spices added at the point of cooking the curry.
Compared to today's equivalents, the sauce back then was always on the thin side and as smooth as could be. Always reddish in colour and plenty of oil floating on top. Nothing else in there other than the chicken which was not always breast meat.
Sadly, nowadays, these places of homage no longer exist (I blame Health and Hygiene), and along with their demise so too has the simplicity of the 70's style madras. As a poor analogy. If the `Greasy Joe's Truck Stop` went the same way, then we'd be hankering after the old time fry-ups. Because let's face it. If you wanted the best fry-up where would you go....the fancy restaurant up the road, or the Truck Stop next to it?
One thing back then. I remember the Asian stores sold large quantities of "tomato powder". Maybe this was used instead of tinned, or puree. Just a thought.
Steve.