i have a 41 shelby built hiawatha that has the same frame as yours,has a tank that goes back to the seat tube,tank is longer than the safty cycle,has 3 gills on the front edge,no horn[i think gambles hardware got it a little less with no horn],top of rear fender bolts to the rear carrier so there is no center render brace,has the hiawatha train badge,wheels look like they are triple steps but im never sure on those,has the big wide chain guard like a aero but is flat no[no gruves?]got it from the og owner who bought it new in 41 to do his paper route,had aero in small letters on the top front of tank,cant think of the name but it had a vertical spring seat like the ones on an areo with the horizontal springs,cant get 2 it to post pics as its buried with a bunch of others,does not have the nultigroved shelby chain ring,i watched over the years,havent seen the exact bike,i think the stig or vince have one thats very similar