For now though, I'm looking at the tiny engine with it's base clamped in the bench vice and trying to visualize a better setup for playing with this little engine. I have an air compressor set to 100 psi or so, and the instructions recommend running this engine on 5-10 psi. Right now I have a piece of rubber tubing running to the engine and I'm using a blow gun in the other end to run the engine. I have to use 3 hands to hold everything together and spin over the engine to get it going. I was thinking some people must have like a heavy base or something they can hook up to shop air, then have a smaller line or two that can have the pressure finely set to run the engine.
I don't know how the guys who build engines handle it, but around my shop where I have air outputs set for everything from driving high-volume pneumatics to dusting off parts, I use manifolds. I have several varieties.
The most common (and not what you really need) is a piece of ø2.00 inch aluminum round bar turned such that I can have one 1/2 NPT input and four 1/4 NPT outputs. I basically have one of these at each machine so I can have flow/pressure for a mister, pneumatic clamps, and still have a blow-off tool.
More to your application, I took a piece of 1.00 inch thick X 6 inch wide HRS bar and drilled/cross-drilled it twice from each edge making a tick-tack-toe (naughts-and-crosses for you on the other side of the pond) pattern. I plugged five of the holes and tapped the last 3/8 NPT for the air inlet. I drilled "down" into the remaining passages (usually five places) and tapped to accept a small pressure regulator. The manifold is heavy enough to (usually) stay where I put it and I have have several different pressure output right there at hand.
When I need particularly stable output flow at some regulated pressure, I use a (about 6 inches long) piece of 4 IPS Schedule 160 pipe that has (L 8X8X.75) angle iron welded to each end. I have an "inlet regulator" (usually set to 150% of my desired outlet pressure) and then an (a ±2%) "outlet regulator" feeding my work. The volume of the pipe acts as an accumulator to minimize pressure fluctuations as I draw air.
Does this help?