Machamp could learn Fissure in Gen 1. Unfortunately, as all Pokemon transferred from the Virtual Console have their Hidden Abilites, Machamp + No Guard Fissure is still an illegal combination. You cannot use an Ability Patch either, as that only changes the Ability from the standard to the Hidden, not vice versa.
You are able to Skill Swap No Guard onto a Pokemon with an OHKO move, however, but this can take a while.