Can you just substitute the new seal/tightness ring and pin, for the yellow tightness ring, springs and old pin? I thought so because the head casting appears the same between older and newer ones, and just the innards changed.
Since the cap only helps in the tensioning of the tightness ring, I do not see how adding teflon helps with sealing ( i'd guess it would hinder it as it adds friction/resistance as to adjust the cap for further tightening). Anyhow, good luck, as it is an excellent pump!