Eric, I would strongly recommend that you use nothing smaller than 30 cu.ft. for you bail out for diving a rebreather. 19 cu.ft. is woefully inadequate for job unless you are in less than 33 feet of water, which in that case, your dil might be enough to get you to the surface.
As for sling systems for carrying off board gas, there are plenty to choose from Halcyon (which has been mentioned), Dive Rite, Oxycheq, Golem, Hollis, etc. In addition to the standard sling, I suggest also adding side mount bungee (used by cave divers using sidemount rigs instead of back mounted doubles) to hold the valve end of the tank up by your ribs, rather than have it drag in the dirt when you are in the water. There is plenty of discussions on this topic over at rebreatherworld.com.
