Most shop compressors and air manifolds at shows require a 1/4 NPT.
You will want a precision regulator large enough to run a good sized steam engine. I will post pictures of these components tomorrow or Friday.
Some quick disconnect fittings and 1/4" hose barbs of 1/4 & 1/8 NPT .
Harbor Freight has good selection of reasonably priced compressors including some that are compact and very quiet. I will add a picture of this as time allows.
edit: you can view some here.
https://www.harborfreight.com/search?q=ultra%20quiet%20compressorI mostly use the 2 gallon Fortress compressors.
I also have A 30 gallon rather loud one in the garage.
Gil