I think the is one of the later style Simmons carbs. I uses the butterfly doors that are slid into place and locked with punched out tabs. I have never seen on with the casting that the name plate is attached to. There are NO drilled passages into it, it's just there. I have an idea what the earlier flappers looked like I am wondering if this one used the brass one? I think the two pins sticking down might have held a bumper of some sort.
"never seen on with the casting" the on should be one.
Add to this, most of them I have seen, the casting on the outside looks the same as the common NH.
I think that one of those pins sticking is a stop for the flapper and the other is just to plug a hole used as a passage hole for a drill bit. Inside the bore there is also a plug. The passage drilled from the top exits in the mixing chamber. Is is intersected by a passage from the choke side.
I've seen a lot of Simmons carbs, but never one like that.
Nether of the pins line up with anything on the bottom. The passage you see at the choke end bisects a hole drilled into the main jet passage. The plate carries the same info as the one Corey shows. Where one expect to see a passage at the throttle butterfly end, there is none. Besides the holes for the throttle shaft the only other is the hole for the heating element. All fuel is coming thru the main jet controlled by the needle and flap. Except for making a new needle, flap, replacing the choke/throttle plates, adding a center drain assembly and gaskets I am close to trying it out! Not seen in the photos I have the float and valve, bowl, main jet, throttle/choke shafts.