It is fairly simple. The earlier Medalists don't have a click "gear" but instead have a "drag disk" that is a bit tricky for hand work but could be done on a minimill easily. The drag is adjustable with the thumbscrew. Because of the way it is designed, the spool can turn freely with minimal friction on the retrieve and then have drag when a fish runs. Here is a photo of one of mine:

- IMG_0825.jpg (156.5 KiB) Viewed 333 times
The Pflueger Gem is another classic reel that is kind of overlooked by collectors but is a beautiful and great fishing reel! It has a very classic click-pawl drag system. The earliest Gem also had a quick release spool that used a crescent latch similar to some Hardy and other reels. Here is a photo of mine:
You can see a standard clicker on the spool and a simple pawl and spring on the back plate. Non adjustable but very functional. Here is a photo of the latch:

Now that the book is done, I am planning to draw the plans and write up the drag mechanisms I make for some of my reels. It is a click-pawl design that has less resistance on the retrieve and more on the outgoing line. It can be made with similar techniques as shown in my book (hand tools) and my goal is to be able to retrofit it on a reel built from the plans in the book! That's the tricky part because of the holes drilled in the back plate - working on locating and designing the spring so it is not visible. Almost have it worked out. I will be offering the parts to make these as a mini materials kit as well. Good spring material is expensive and can only be purchased in bulk (at least I have not found a source for smaller quantities). I had to buy 100' of the material but it makes a great spring. You can use common music wire from the hobby shop too if you temper it properly. (there is a thread on this forum on annealing and tempering steel - search "temper" in the search bar above and click the Spring Material link).
I have a few customer reel orders to complete first though.
cheers,
Michael