Given there is no separate part number for it in the '51 Kaiser Parts book, the answer is that it is not removeable. I've had the pin fall off of my Henry J drums too - it's welded on and intended to be permanent. If one is missing, the wheel of course can be installed and the car can be driven but it's a pain to replace a wheel without a guide pin there. Looks like you'll need to replace the whole drum. The drum on '51-'55 Kaiser should all be the same.
