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%20compressor
I mostly use the 2 gallon Fortress compressors.
I also have A 30 gallon rather loud one in the garage.
Gil
I just bought an Ultra Quiet California Air Tools compressor with aluminum tank and long life motor, only 60 decibels, I love it!! You can run it in the living room and talk to the person sitting across from you
https://www.californiaairtools.com/industrial-series-of-quiet-compressors-industrial-grade/cat-8010alfc/