I am unfamiliar with Greenier safeties but it is true trigger block safeties are generally thought to be not as "safe" as striker type safeties. Perhaps if a quality trigger block safety gun was dropped off a cliff it might be jarred enough to discharge, but in most hunting situations they are considered safe enough. The safety issue of placing the gun off safe to unload the gun is, I suppose, real enough. I've had to do it with my Springfield since Dad installed the 2-position Buhler style safety back in 1962. I'm in the habit of pointing the gun in a safe direction at ALL times so it would never be an issue. Haven't had a slam fire yet. It's possible I guess but extremely unlikely.
For any of us who are experienced, two safeties is unquestionably redundant. Certainly, if a 3-position Model 70 safety is added, the historic value goes out the window. And the Greenier side safety definitely becomes redundant as operating the Model 70 style safety would be just as easy, if not more so, than Greenier. No point in keeping it. As I said, I think the least historicly impacting improvement would be go to a commercial Mauser shroud, toss the flag safety, and drop the scope mount down to something more user friendly.