I'm going to correct myself and say I'm almost certain this is a '40. The ad Mark posted does not show up in the Monark book. Speaking of the book the reference I'm using is the 2012 Revision and all page numbers will be from that book. So why do I think this is a '40? As I mentioned before the tank graphic is one thing that points to '40 - '41 although this graphic actually does appear in '39 on at least one model (Model GT 497-top of pg 39).
Most '39s have the serial number punched crudely into the frame tube underneath the crank hanger. From '40 on most are small, uniform numbers on the left rear drop out.
The Model 493 GT is shown directly under that and is what we generally refer to as the 26X. Notice both of these bikes have the 'pencil' spring fork which is a '39 only feature of all Monark models using a spring fork. Another feature peculiar to '39 is the wedge type seat post. Notice from '40 on in the book where all the racks attach to the seat binder. Most '39s use a McCauley nine hole with the universal front mount.
A key thing that points to '40 or later on this bike is the badge. In 1940 the Airman badge changed (see pics below). Also most, but not all, '39s had flat fender braces. The book does not even show a Speedster type model until the '40 Airman Jubilee "Streamline" Specials (pg 41). Lastly the bottom of page 42 shows the "Speedster" but you will notice a lot of '41 only features--namely the guard, fenderlite, and "extra deep crescent fenders".
Lastly I want to publicly apologize to Chad for my initial comment which came across a little snarky. Chad stepped up to the plate, swung, and hit a home run and I commend him. Chad has certainly spent the time, money, and energy on this crown jewel and I'm grateful that this bike was not restored as the hobby would have suffered for it. V/r Shawn
View attachment 716826
1939 Airman Badge
View attachment 716827
1940 Airman Badge