First off, there is no "Model 70 Commander" or Series 70 Commander. Series 70 was actually a specific model name of a 5" gun. These guns actually said "SERIES 70" on the slide or something to that effect. What you have is a Commander in either the light weight or Combat variety.
As for the grip safety, that is obviously not original to the gun and has not been fitted properly. Is it possible for you to post pictures? There are different makers of grip safety and some fit differently.
I can't think of what the slide being off/on would make a difference unless something is totally jacked up.