Vintage Double Hose

Trying to remove Nemrod valves from a set of triples. I'm a hair away from damaging them. Valves are on tanks last hydro's in '69. Obviously like to keep the original triple, but feel like I'm about to do damage. Have tried using Teflon padded wrenches and rubber mallet and wood shims. Bottles are Teflon taped with minor corrosion.
Help?

I remove odd shaped valves (that won't accommodate a wrench) by taping 1x2 wood pieces the length of the jaws in my bench vise, then turning the tank upside down with the valve being held between the wooden "jaws". You can use thicker boards and even shape the wood somewhat to match the valve shape. The tank can usually be turned with a large strap wrench or chain tongs.

The patient survived unscathed. I loathe using the bench vise on vintage pieces, but it was a do it or forget it. Thanks for the support.