Go with the aftermarket commander style. The hammer need only have the full cock and 1/4 cock (two-position) function. The Springfield 3-position design brings nothing of value to the operation of the pistol. Just make sure you install a 70-series type hammer. 70-series will ensure the hammer is locked - and cannot fall on the firing pin - in the 1/4 cock position. FYI -- I build 1911's and I am a credentialed gunsmith.
The SA 3 position hammer is sort of unusual. Below on top is a Colt hammer with the quarter shelf. Know you have that if you pull the hammer back and it stays but drops when you pull the trigger which does not happen with a half cock position. In the middle a Colt hammer with a half cock. On the bottom a SA hammer (out of a RO) with both the quarter shelf and half cock.
And another view of the three hammers in the same order.....
The quarter shelf hammers have nothing to do with a Series 80 mechanical firing pin safety. Colt also uses them on many of their pistols with no mechanical firing pin safety. Also other manufacturers which use the Series 80 mechanical firing pin safety do have a true half cock.
Now the new "Series 70" colts I have with the quarter shelf hammers do have Titanium firing pins.
The Safety Stop is a flat, shelf-like surface on the hammer which functions automatically. It will engage the sear in the unlikely event of primary sear notch failure. This will prevent the hammer from falling fully forward unintentionally and will insure against uncontrolled automatic fire. It also prevents the hammer from striking the firing pin should your hand slip from the slide or hammer while cocking the pistol, provided the hammer is rotated past the Safety Stop. It is located such that when the sear engages the Safety Stop, the sear can be disengaged by squeezing the trigger. It falls because the sear slides over the flat part of the safety stop to release the hammer. This is intentional but will not allow the pistol to fire. It will not fire because the hammer is almost fully forward when it is released from the sear. The Safety Stop is not a manual safety and should not be engaged by hand. Do not carry the firearm while Safety Stop is engaged.