Your bike is actually quite complete and correct as it stands. The model was first offered in the Fall 1937/ Winter 1938 Mongomery Ward catalog as the “New Hawthorne Twin-Bar Model” and was produced for Montgomery Ward by Monark.
Features that distinguish the first version are the use of the Monark chain ring mounted chain guard and the Troxel Streamlined saddle that is essentially a tool box saddle without the tool box. The model was offered again in the Spring 1938/ Summer 1938 issue of the catalog but with a standard chain guard and saddle.
In the first catalog the bike is shown with the fat Delta torpedo headlight that is common on Rollfast bikes and is the same as the early round “Zep” headlight without the fin. The bike is also shown with the cast Torrington bevel-lock stem. The second catalog version depicted has a steel riser stem but has added the later, ten sided version of the Delta produced, Hawthorne “Zep” light.
Your bike looks like it has a Delta Winner headlight which I believe is a bit later than the bike. The stem is also possibly a change-out as it is not the same as either unit depicted.
The good news is that these bikes never used a tank and there is no tank extant that will fit the frame, so in having the saddle and the chain guard you have the two difficult parts for the bike.
The catalog lists them as being offered in red or blue and I can see the original paint pattern is still evident under the surface corrosion.
As to how these bicycles vary from the Monark 5-Bars; the main difference is that most of the steel Monark 5-Bar frames have a straight lower top tube and are designed to accept a teardrop shaped hanging tank although they were marketed with or without tanks. The second difference between this and the contemporary in-house Monark frame is the Monark frame has doglegs pressed into the seat stays near the upper fender bridge while the seat stays on the Hawthorne version flow in an unbroken arc from the head tube to the rear wheel receptor plates.
Interestingly the pioneer of this frame design, Monark fell into disfavor with Montgomery Ward after 1938 and the aluminum frame Hawthorne models were dropped from the catalog. Apparently, MW felt they had something with their steel 5-Bar models and continued to offer them using both H.P. Snyder and Cleveland to fill the manufacturing gap. All three manufacturers versions of the early (Fall 1937 – Winter 1939) 5-Bar differ substantially in the construction details of the frame which is especially noticeable near the crank hanger.
For Spring 1939/ Summer 1939 the 5-Bar models were completely redesigned and moved to the top of the Hawthorne model line (The earlier versions were always a mid to low priced option in the line.) The Late versions were produced by both Snyder and CWC with differences and these are the bikes that used the special twin-bar Zep Tank.