Consider yourself lucky that it is belt driven! Brownies was playing catch-up to the AirLines direct drive unit at that time and having all kinds of problems with the Chinese copy of the Thomas compressor parts they were assembling their direct drive units with. I believe your unit is a 3-60 and uses a Thomas compressor block. Unless you can find a Brownies dealer in your area that actually does service, you may have to go to three different places. One to service the honda, one to service the compressor block and a dive store that can service the hookah regs. The hookah regs may be Sherwood second stages, but the springs are rated to around 60 psi. Typical scuba second stages work with springs rated around 140 psi.
If I recall correctly, that unit was selling for around $2300.00 new at the time. I worked for Brownies from '92 to 2000, but not with the L.P. stuff.
Regarding the honda, hopefully they ran the fuel out of the carborator before storing. Probably too much to expect that they drained the fuel tank. If not the fuel may have "gummed up" the carb beyond the point of being able to repair it.
Personally, I would disconnect the spark-plug wire, make sure the fuel "shut-off" is closed and the carb bowl is drained, then pull the cord slowly to make sure everything rotates smoothly.