Retrofit Oil to Gas or new boiler

Hi - I have a Weill McClain oil boiler that I would like to convert to gas.  Boiler was installed in 2002.

two options: Carlin or Beckett gun conversion, or replace entirely.  Is the gun efficiency lower than a replacement? In interested in economic merits.

also, this boiler is an indirect water heater.  So I'm breaking that bond as well.