That screw may have changed over time, but I checked the 37 I sporterized a few years back, Serial Number 04985, and that front trigger guard screw is the same diameter and pitch as the two action screws, the oddball 7/32" x 28. I remember well, because the previous owner had replaced the action screws with some stainless cap screws, and I ended up using a couple of Rem 700 action screws by re-threading them to 7/32" x 28 and turning down the heads. In retrospect, re-tapping the receiver to 1/4"x 28 would have been much easier. Also, since I restocked the rifle, and the TG nut was embedded into the old target stock, I ended up using a thin brass nut for the TG screw:
BTW, the Miracle Trigger will look like this. I'm guessing that's what's in that rifle, unless it was replaced:
TBR