I don’t know that any of this is early punk. Maybe Patti Smith? You’re looking for Ramones, early Clash, Bad Brains, X, Dead Kennedys, Black Flag etc. Maybe Joy Division. Replacements? Elvis & the Talking Heads are more post-punk.
Judee Sill- anything
Stevie Wonder - talking book, Fullfillingness…
The Wipers- Is this Real, etc. etc. They rock harder and with more melody than any band ever. I know you don’t believe me but you haven’t heard them. They did Youth of America too.
I second these with gusto:
Big Star - Sister Lovers, etc.
Nick drake - anything
Scott Walker - Scott 4
I was listening to Stevie Wonder’s Songs In The Key Of Life, inspired by this thread, and thought that soul music is kinda underrepresented in this thread, which is a shame since the 70s, especially the first half, was a great period for soul. I remember Stevie Wonder, the Meters and Sly And The Family Stone being mentioned, but there’s so much more, so here are some suggestions:
Stevie Wonder - everything from Music Of My Mind to Songs In The Key Of Life, that was a magical streak of albums
Marvin Gaye - What’s Going On, Let’s Get It On, I Want You
The Temptations - All Directions
The O’jays - Back Stabbers
Al Green - Let’s Stay Together, Al Green Is Love, The Belle Album
Curtis Mayfield - Curtis, Roots, Superfly
Bobby Womack - Across 10th Street
Aretha Franklin - This Girl’s In Love With You, Spirit In The Dark, Young, Gifted And Black
And some New Orleans Funk and R’nB:
The Meters - Look-Ka Py Py, Rejuvenation, Fire On The Bayou
Dr. John - Dr. John’s Gumbo, In the Right Place
I think you would like
Lido Shuffle - Boz Scaggs
Eagles - almost any of their '70s output
The Who - Whos next
Steely Dan - Aja is the standout but Royal Scam is also worth noting
You could pick on a couple of Led Zeppelin albums, Led Zep IV for example.
Gordon Lightfoot might also fit in if you like a country sort of feel, although it is not country music at all, more folk oriented.
He wanted lesser known stuff.
Hey!
How could Talking Heads be post punk in 1975?
Costello was new wave but not seen as punk (In retrospect only) cause of his craft and experience, not post punk at all.
Replacements are Alt pioneers.
Dixie Dregs
Ozark Mountain Daredevils
Molly Hatchet for late 70’s
Chris Spedding Hurt Album 1977
The Guess Who American Woman Album 1970
Excellent call on both of these.
mmm
I don’t believe I’ve seen Dan Hicks and the Hot Licks mentioned yet. See if you can find a copy of “Striking It Rich” or “Where’s The Money”.
Tom Waits Nighthawks at the Diner , top of my “wish I was there during the performance for the live album” list.
I do really like the majority of stuff that Supertramp put out in the 1970s. Crime of the Century and Even in the Quietest Moments… deserve special mention.
Right on. And Last train to Hicksville is right up there too.
Hey nuttin! No matter how you interpret that, I said you have your moments. 
The OP said they didn’t want to go full disco, but Reggae wasn’t mentioned. If you’re game, anything backed by Sly and Robbie (which is a hell of a lot of stuff, they worked with everyone at some point), is at least listen-able in a poppy way. Some of it is transcendent. They did most of their work in the 80’s, but they got their start in the 70’s, and it’s always had a 70’s flavor, to me.
Rickie Lee Jones, **Rickie Lee Jones **
Lee Michaels, 5th
Little Feat, Dixie Chicken
Good one. Also “Sailin’ Shoes“. And in a similar vein, almost all of Ry Cooder’s 70s albums are fine works.
Agree with pretty much all that have been posted.
Just would add Jethro Tull, King Crimson, Procol Harum, and Uriah Heep.