I know it is a 4.2, but need more info on builder. It has an aluminum colored case and a Sachs crank. The rear of the case has been relieved and there is no provosion for a smoke tap. Also, the prop adapter has a threads on the inside, and a dimple machined into the end of the crank. Has a C&H spark-coupled ignition system.

here is another pic:

one more pic:

Its a Bryons 4.2. They were made by A&M or some by Planes +.

Thanks for the quick info. I had a suspicion that may be what it is. Has a lot of the old A&M traits(sure glad it has a Sachs crank), but that prop hub threw me. I guess that is for the scale props Byron had?
Thanks

The threads in the hub are for the puller used to take the 2 blade prop hub off to use the Byron 3 blade prop....