My search (of GR-618) showed the regulator is a Gas-Flow GR-618 and is an 18# regulator. Here's one of the links with the info:
http://www.wildcatcamperforum.com/t3921-regulatorsagain
If you read further down in the link, someone reports that the GR-618 is no longer made and is replaced with a GR-630 (30psi) regulator. This is similar to many of us who have replaced the 18# Marshall with a 30# marshall on the far side (passenger side for my rig). The changeover on my rig is on the driver's side and the far side plugs into one of the connections. The other connection of the changeover goes directly into the QCC connector (the big one you tighten with your hand) and into the propane bottle on the driver's side.