I just talked to Victor customer service. I called them to find out if I can use
their medium duty single stage acetylene regulator, no. SR-260A, on a propane
tank. They told me the following:

Both acetylene and propane cylinders use a CGA 510 connector (aka a POL fitting)
so you can generally use an acetylene regulator on a propane tanks but most
acetylene regulators are set up for the range 2-15 psi so if you plan to use
more propane than that you should either get your acetylene regulator modified
to use a stronger spring and different gauge or you should use a regulator set
up for propane. In addition, once you use a regulator for propane (which leaves
tarry residue inside) you should not go back to acetylene with that regulator.

As this has come up here before, I thought I'd pass this along for comment or FYI.

GWE