Aloha, Bruce!
Yes, that little tube that is attached to the underside of the downtube on your 41 BFG Streamliner, is for the little rubber fork bumper stops.
If you have an Ace/Crown Hardware store in your area, check their Hillman fasteners supply, for rubber stops and bumpers.
They have a suitable replacement bumper that fits that bumper tube pretty well.
The original was a cylindrical shape with a cap type head on it, which unfortunately isn’t made any more.
The type that Ace/Crown sells, is more of the type meant to be pulled through a hole in a piece of sheet metal.
So not completely ideal, but once installed, they look the part, and serve the same purpose as the original intent.
I’ve shaped the part that presses into the tube with an Exacto knife just to improve the fit.
It would be beneficial for one of the grip/pedal block makers to reproduce these bumpers, but as far as I know, no one has.