The slaggers were all similar but not all parts interchangeable. The Rogers of the dual intake variety seem to be the best performers. These engines had a front rotary valve and a sideport inlet on the rear of the cylinder. They will run, but they need so much oil for avoid, or should I say slow down, their self destruction that they need hot ignition. My dad tells a story of he and a friend and a Syncro B-30. Dad lived in Detroit where the Syncros were built. His friend bought a B-30 and they tried for days to make it run to no avail. So as a last resort for 2 kids that were out of ideas they went to the "plant". In the back there was a doorway into the repair area. They hung around there until some grumpy guys asked what they were doing hanging around there. They showed him the engine and explained the problem. He softened a little and took the engine and had them go in. There was a long bench along one wall with test blocks and he quickly set the engine up, fueled in and in a few flips had it running. They were happy and headed back to his buddy's place and put it in the model. It never ran again, or should I say they could never get it to run again. looking back Dad says he's sure it was poor ignition and that's probably what it was.
They are way down in power for .29s, maybe about what an old Fox .10 puts out, a little more for a good one. SAM has a slag even and its fun watching guys fly or try to with these things. There was one guy that used only Rogers and he won pretty consistently mostly because he could actually start and run them pretty well.
I have a few, a Thor I build from a set of old castings and parts Dad passed along to me. It runs as well as any but that's not saying much. The bypasses are so small in them I had always thought about "porting" one to see if I could get any more out but I've never gotten that involved. Interestingly, Syncro had a version with 2 very fine iron piston rings which seems to have been a good idea except the aluminum cylinder just wouldn't hold up. Dad was experimenting with aluminum rings when his vision suddenly got very bad, now all his projects have become mine to finish.