These aren't thoroughly catalogued anywhere.
Courtesy of mycomicshop, comics.org, my own collection and a few blogs, here's a list of the 7" X 10" comic books from Power Records:

PR-10 AMAZING SPIDER-MAN Gil Kane/Romita Sr art, Man-Wolf story, r AMAZING SPIDER-MAN 124 (1974)
PR-11 INCREDIBLE HULK Trimpe art, r INCREDIBLE HULK 171 (1974)
PR-12 CAPTAIN AMERICA Sal Buscema art, r CAPTAIN AMERICA 168 (1974)
PR-13 FANTASTIC FOUR John Buscema/Sinnott art, r FF 126 (1974)
PR-14 FRANKENSTEIN Ploog art, r (in edited form) MONSTER OF FRANKENSTEIN 1-4 (1974)
PR-15 DRACULA Colan/Palmer art, r TOMB OF DRACULA 19 (1974)
PR-16 MAN-THING Ploog art, r MAN-THING 5 (1974)
PR-17 WEREWOLF Ploog art, Colan art, r MARVEL SPOTLIGHT 2, WEREWOLF BY NIGHT 14 (1974)
PR-18 PLANET OF THE APES, Virgil and Nestor Redondo art (1974)
PR-19 ESCAPE FROM THE PLANET OF THE APES, Virgil and Nestor Redondo art (1974)
PR-20 BENEATH THE PLANET OF THE APES, Virgil and Nestor Redondo art (1974)
PR-21 BATTLE FOR THE PLANET OF THE APES, Virgil and Nestor Redondo art (1974)
PR-22
PR-23
PR-24 AMAZING SPIDERMAN "Invasion of the Dragon Men", Buckler(?)/Giordano(?)/Austin art, new story (1974)
PR-25 STAR TREK "Passage to Mouav" Adams/Heath art (1975)
PR-26 STAR TREK "The Crier in Emptiness" J. Buscema/Giordano art (1975)
PR-27 BATMAN The Joker "Stacked Cards" Adams art (1975)
PR-28 SUPERMAN "Alien Creatures" Swan/Giordano art (1975)
PR-29 SPACE 1999 "Breakaway" adaptation of first episode/origin, Heath art (1976)
PR-30 BATMAN with Robin, Manbat, partially taken from DETECTIVE 400. Adams/Giordano art (1976)
PR-31 CONAN, Buscema/Adams art, 20 pages, reprinted with 3 new pages as CONAN THE BARBARIAN 116, Nov 1980 (1976)
PR-32 SPACE 1999 "Return to the Beginning" Heath/Giordano art (1976)
PR-33 SUPERMAN "The Man From Krypton" Buckler/Giordano art (1976)
PR-34 SUPERMAN "City Under Seige" Andru art (1976)
PR-35 WONDER WOMAN "Secret of the Magic Tiara" Buckler/Adams/Giordano art (1978)
PR-36 HOLO-MAN Joe Geilla art (1978)
PR-37 ROBIN HOOD Jack Sparling art (1981)
PR-38 MOBY DICK
PR-39 HUCKLEBERRY FINN Sparling art (1981)
PR-40 DAVY CROCKETT Buckler/Giordano art (1981)
PR-41 ROBINSON CRUSOE Almendola/Giordano art (1981)
PR-42 20,000 LEAGUES Buckler/Giordano art (1981)
PR-43 LAST OF THE MOHICANS
PR-44 GULLIVER'S TRAVELS
PR-45 STAR TREK "The Dinosaur Planet" (1981?)
PR-46 STAR TREK "The Robot Masters" Sekowsky/Giordano art? (1981?)
PR-47 LITTLE WOMEN Giordano (and Infantino?) art (1981?)


The ones left blank I could find no information on. Even in the back-issue lists in the books themselves these numbers are not shown. Possibly they were numbers assigned to books that were not ultimately released, aborted projects.

There are also a number of 12" X 12" LP record album sized projects, I have a STAR TREK one, but like many, has no comic book included, just cover art (by Neal Adams) and the record itself. Some LP's have comic books, some don't. The comic book size ones are all comic books that include a smaller 45 rpm record.