I don’t really know much about it, but I do have a complete set.
The mask is part of the Scott-Hydropack system. Scott has been around for a long time making SCBA for firefighter and other hostile breathing "Hazmat" environments.
Scott is now owned by 3M, and makes the Scott Air-Pak, which is a firefighter SCBA system:
"3M™ Scott™ Air-Pak™ X3 Pro SCBA"
The Scott-Hydropack consisted of the full-face mask with demand valve, the first stage, the cylinder (mounted with the valve on the bottom, like a typical SCBA), and the back-pack.
Here is some information:
The Hydropack was a direct competition to the Aqua-Lung, but AFAIK it was a lot more expensive.
BTW, the original Aqua-Lung was the name used by US Divers for the complete system: “the regulator, tank, and harness” made a complete Aqua-Lung system.
I have been looking for more information on the Scott Hydropack (including manuals, diagrams, and more history), but I am still looking.
I need to service and dive the one I have.