Another showbiz/music candidate for a MoD article would be Jim Seals (Seals and Croft.) He has Dallas roots, I believe he's down in the TX Hill Country today. John Ford Coley would likely know where he is since "England Dan" - Jim's bro. was his musical mate back in the day. I don't know him. Here's and old Tx Monthly article:
https://www.texasmonthly.com/the-culture/secret-oil-patch-roots-summer-breeze/
Angus Wynne, I know the name from Six Flags, that was the 3rd's dad. Your AW, 3rd I looked him up on wiki. What popped in my head when I saw his bday was 12/25/43 very close to Jim Morrison (12/08/43) - a former neighbor (3 blocks away) - same HS, 10 year apart. I was too young when he was here in '58-'61.
I never really was involved with the large-scale "festival" world which have largely been killed off by amphitheaters with a more controlled environment, and ample facilities. Also now there are annual festivals like Bonnaroo and Cochella with permanent sites. Getting permits to put on a one-time show is close to impossible - it almost killed Woodstock in '69 - the concert was moved 50 miles just weeks before to Bethel NY - Max Yasgur's farm. They tried to do a 50 year re-do last summer and were unsuccessful. The Woodstock festival site is now gentrified and has a beautiful concert facility and has the "Museum at Bethel Woods" memorializing that weekend. I know the museum director there.
I looked up Angus' Dallas Pop 1969 festival. Unbelievable line-up of talent.
https://en.wikipedia.org/wiki/Texas_International_Pop_Festival The only acts that were there that I've had contact with are Carlos Santana, Sly and the Family Stone (now The Family Stone, Sly apparently is in a world of his own) - Dallas roots there, and distantly Led Zeppelin via The Yardbirds - the predecessor of LZ.
The festival that really started it all, the Monterrey Pop Festival 1967 was produced by another that went to my HS way before me: John Phillips - "Mamas & the Papas" (along with Lou Adler.) I was just too young to have that experience.
Trivia: Woodstock was such a mess and so poorly managed, almost a comedy of errors. Time ran out on the pre-concert construction so the decision was made to build the stage and not complete the fencing. The turnout was huge since with no perimeter effectively the concert was FREE to all comers. it was a big financial loss for all the investors. The silver lining was the film that Michael Lang authorized gave the festival mythic status. The profitability came, long term, from the licensing of it's famed logo: with doves on the guitar neck and the words "3 days of Peace and Love."