Thanks for the follow-up - your piece looks to be a 1st Model 6th Variation (1937-39) - with the address block stamp moved to the right side of barrel and the cylinder release moved to left side of frame; most likely mid 1937 - from the s/n.
One of the most common problems with these older Sportsman pieces - is exactly what you've experience - loose screws on the rear sight block. One of the most commonly sought replacement parts is the rear sight blade - which has fallen off due to loose screws. LocTite should work for you - do it before you lose your sight blade.
The condition of your piece is similar to the physical condition of my 'range' Sportsman - the other ones (which have taken 16 years of search and upgrades to add to collection) are just too dang nice to risk screwing up.
You're welcome and thanks for thanking.