80s versions
Well aside from Optimus Prime generally refusing to kill a human. This could still go either way.
80's Prime is slower than current Prime but has strength feats and sheer durability. His fire power is conceivably bigger but unfortunately less accurate.
80's He-man isn't slow but is not the samurai skilled barbarian like his 90's showing. His 80's strength would scale (lacking constancy, he has held up castle greyskull) while 90's seemed just below claiming to be the hulk. While there sword of power can deflect weapons fire, neither were able to parry a blast bigger than them.
Prime shoots at Addams feet the truck rams him. If that doesn't work then Addams sword would need to find itself in Primes belly movie style. As unlikely as 80's he-man is to win against Megatron, he actually has better odds taking on 80s Prime.
During a commercial break, he-man's battle cat malls roller giving He-man the opening to do the deed. However once seeing the painful backlash on Prime realizes he is indeed a living being. He-man can not bring himself to kill Optimus. MK friendship at its finest...
IDWs Megs would shoot 90s Adam, then the tiger he road in on, and stomp the remains. He-man's rage (he would survive the first shot) would get a scar on Megatron but ultimately prove futile. Megatron claims the power of greyskull for himself.
personally I'ld rather see
Brawn face off with
Man at Arms