Yeah, it was supposed to be Frankenstein and not Kong that fights Godzilla in the original I believe. Hence, the lightning bolts powering him which makes no sense.

The original King Kong vs Godzilla is such a fun, goofy movie and it's one of my favorite Godzilla and King Kong movies. I know this sounds like a horrible idea that makes no sense on paper but just have Rick Moranis go all "Honey, I Blew Up the Kong" and let them fight, damn it. I would be there opening night.

I had the pleasure of meeting Mr. Hoffman at NYU about a year before he
died. He came and talked with a group of students that included myself
about his time at NYU, his career, working with certain actors and
directors like P.T.A. and he gave some really great advice.