Is this a '41 Colson?

[SKPC]

Yes, BB main serial number stamp is a Shelby R number. So pretty sure @Freqman1 is correct on year and that the diamonds & 41 are added. Those chain guards were used on Shelby bikes for a few years but don't know which. What is interesting about this one is the curved down tube. Other R streamline frames have straight down tubes Hmmm...

Also noteworthy is it seems the R serial number "streamline" frames were both non-Y and pinched like R586328 below. The Y streamline "R" frames now seem to have had two different down tube styles, straight and curved. Three others were a straight bar, a camelback and a step thru women's' (so far). 3 different seat clamp styles as well: frame-pinched, early thin collar style and the women's longer collar style. The volume of examples of R frames is low, so I will add your frame to the Shelby Serial thread.

R619xxx

 

[Freqman1]

I looked up '38 Shelby and did not see a model with this chain guard? Guessing this is a lower model? Sprocket looks like '41 and newer. I also noticed Western Flyers and Hiawathas in search. I'm assuming Shelby made those?
It's apart and ready for paint.... thinking Flamboyant lime....

This bike is not factory correct. Things have been changed over the years.