Hi
Here are some pictures for comparison to help (?) pin down the manufacturer of your frame
The first photo is a composite showing the recently found Westfield Elgin Moto-balloon fork crown on the extreme left and your fork crown on the extreme right. In the middle a Westfield fork is shown next to a Monark fork. While similar the fork crowns are discernibly different and the fork crown on your bike matches the one used by Monark.
The second photo shows the rivet placement in a Monark Fender (left) compared to the rivet placement in a Westfield fender. The rivets don’t show in your photos but this is another thing to look at.
Lastly I have taken photos of four dropouts. The upper left is from a Westfield frame. The Westfield dropouts with ears from this period that I have looked at have a notch between the dropout slot and the drop stand hanger bulb. The dropout in the upper right is from a late Murray Ohio built Elgin. These dropouts are very different and used a special separate tensioner to pull the wheel rearward and are not stamped for the more traditional locator bolts. The bottom left is the earlier and more conventional Murray Ohio dropout and the dropout in the lower right is from a girl’s Monark 4-Bar. Colson dropouts are also similar but I didn’t get to photograph one.
At this point I would say that the chain ring and the fork point strongly toward Monark as the manufacturer. The fender bridges also are similar to those on some steel Monark frames. The heavy lugs may relate to Monark’s use of cast aluminum lugs on their aluminum frames but that is a stretch. The lugs and the seat cluster still look more like those commonly used on Canadian CCM frames (see the Massey) or later on Worksman frames.
The serial number is inconclusive but it seems to rule out Westfield or CCM as those two systems are known. The serial number has little in common with the Early Monark frames I looked at but two are from the Aluminum series an the other is a later 4-bar frame.
The dropouts are also somewhat inconclusive. While they don’t have the Westfield notch,
they are also very differently shaped than the later Monark 4-Bar dropouts.
At this point my money is on Monark, but I don't feel there is enough proof yet to be certain.
Phil