Was there ever a place in England called Cumbria before the county came into being in the 70s?

Yes. It's an ancient Latin name, a cognate for the Latin name for Wales (Cambria - Cymru in Welsh), reflecting the fact that historically Cumbria was a Brythonic (Celtic) land much the same as Wales and Cornwall, and remained so a lot later than the rest of England when it was conquered and settled by the Anglo-Saxons.

Cumbria and Cumberland mean the same thing anyway, it's just that one is Latin while the other is English. Cumbr = Cumber (both come from Kombroges - the name the local Celts gave themselves), while -ia is a common suffix in most Indo-European languages that means land. Hence why so many country and region names end in -ia or something resembling that sound.

YES....Celtic...

Yes, that is why the County Council is called Cumbria,

Yes but it has had variable borders & rulers/owners through the last 1300 years.

https://en.wikipedia.org/wiki/History_of_Cumbria

you are talking about the Cumbrian mountains in Scotland where Britains tallest mountain is Ben Nevis so yes as far back as who knows when Cumbria has existed part of Scotland