The misattributions to Don Segall on the GCD for these books, coalescing as far as anyone can tell out of thin air, originated decades earlier with me, back around the time I misidentified some non-William Woolfolk stories as Woolfolk's. I was correct in making the leap from these Dell stories to the Tower ones, but started from a misidentification of the writer. From what I can see now, Don Segall worked at Dell up through the middle of 1965; these are from 1966-67.
DJ Arneson not long ago recalled writing a comic's entire first issue for Tower, an "Undersea guy." He actually wrote two issue's worth of those
double-sized books, going by the style. He remembered writing the Dell monster superheroes specifically. His other series like the Monkees and Dark Shadows (to name only two) never got misattributed.
An early warning sign for Arneson's writing is "Great Scot"
(although I've seen him use the latter once or twice). The full page
from 1966's bookstore comic THE GREAT SOCIETY COMIC BOOK, on which he
and Tony Tallarico
(though not ghost-penciller Bill Fraccio) got cover and splash credits;
the tier below it is from FLYING SAUCERS 1, art by Chic Stone.
Scripts by DJ ARNESON, not
Segall, at Dell
DRACULA 6-8 (reprints 2-4)
FLYING SAUCERS 1-4
FLYING SAUCERS 5 (reprints 1)
UNDERSEA AGENT 1-2