I have no idea who made that reel for J.C. Higgins. I've never seen one like it sold by a different company, either, although Higgins also sold the model 400 which looked similar only black. They were both sold in the mid '60s. I doubt it was a trade type reel since there are no similar examples that I have ever seen sold by different companies. Interestingly enough, I don't have either of those models so I've never explored their inner workings.
There are a lot of older reels, and a few newer models, that have a locked anti-reverse. Langley/Zebco quickly come to mind. Here's a picture of a permanent or reoccurring A/R that functions by use of centrifugal force, gravity and a flip wire/spring. The “dog” is free moving with a notch in the middle of the outside edge and positioned on the back of the rotor cup so that when the reel/cup is in forward rotation it clears the stud located at the bottom center on the front of the body housing. On some models there's a small vinyl tab clinched into that notch. When the rotation is reversed centrifugal force or the trip wire flips the “dog” the opposite direction, and because the obstruction/stud is located at the bottom of the housing, gravity helps maintain the correct position until the “dog” comes in contact with the stud, stopping reverse rotation. There can be a varied amount of slack, which might be fairly large if the “dog” is far away from the stud, that will need to be recovered before the handle ceases reverse rotation. This type of A/R was used by Langley, Zebco, A & F and a few others with various modifications throughout the years.
Open yours up, Joe, and see what makes it tick, then share your finds with us in a few photos. That's what makes this such a fun and enjoyable hobby!
Now go take a ----. 
Oh, BTW, if you have an extra screw it probably came off your furnace or AC. 
Al's registered here and a regular contributor. Maybe it's a mistake or glitch, you should contact him and get it straightened out.