I'd say on the whole they DO have to be from the 70s! I'm subjective, I know, but for me the prime phase of the folk rock scene (if indeed that's what you're after) ended about 30 years ago: Steeleye and Fairport called it a day, albeit temporarily, with Live at Last and Tipplers Tales. The Albion Band gave us Rise up Like the Sun, then Lark Rise, then...

When these bands reconvened in the 80s they all to an extent modernised their sound, I suppose everyone wanted to be contemporary and fresh, but to my ears the albums from that period just sound plain awful now. Only Steeleye really stuck with the trad songs (again, if that's what you want).

Anyway, this isn't answering your question. Try 5 Hand Reel, Folque, Malicorne, Spud and Fungus. Maybe also Jack the Lad and Scafell Pike.