Discuss Bob Suffolk's answer to: What diameter drill bit would i use to clean a #48 propane orifice

If memory serves, the old numerical schedule works out about .076".  Note that propane cylinders operate at 1/3 higher pressure than LNG cylinders.  Although American cylinders are required to have left-hand threads on all fuel connections, and right hand threads on all oxidizer or inert connections, that does not necessarily apply to Canadian tanks built before 1988. 

If the amount of rust on the tank in your photo is any indicator of the condition of your tank, I would be most hesitant to keep it.  Most propane jobbers will trade out your old tank for new, often without charge if you sign a contract to buy your fuel from them.

Disposing of old rusty fuel tanks takes specialized equipment and training.  This is not something a do it yourselfer should attempt.