Centerflag Inline reg info?

[lew]

Can you look down the bore from the tank threads? That should tell you what you need to know (it's been a loooong time since I've messed with that reg).

[Olsson]

When the both bolt heads are flush, as in your photo, it is off. To turn it on, you press firmly on the larger of the two bolt heads. The smaller bolt head will protrude very noticeably when the reg is on. Also, when you turn it off - obviously by pressing on the protruding smaller bolt head, it will bleed the pressure with a most satisfying, quite loud "pop".
As for the screw in the dovetail rail, I cannot say. I have, however, noticed with several different tank regs of the time, that there seemed to be a lot of minor differences for the very same model of reg, such as an extra HP-outlet, a burst disc or not, etc.

[MrKittyCatMeowFace]

thwank u

[flyweightnate]

Regarding springs - look on McMaster for Die Springs, and see if any are the same dimensions; they're typically color coded for different strengths. More coils means softer (for a given wire size), since each coil needs to bend less per inch of travel.