My only Mego customs as a kid were to make the invaders. Sub-Mariner was simple, put Spock's head on any figure that had the blue underwear/trunks. No winged feet, but I could make do.
Yeah I had the Spock/Submariner (Sub-Mareeener) as a kid with Robin shorts to boot. I had to reenact my FF treasury edition somehow. Then I realized, I didn't have the FF.
The Meet was a real blast in terms of selection, I left a great of money there and still all the way home I kept thinking "Why didn't i grab *****?"
Such is collecting I guess...