Pulled my PRW rockers out and they have the same script on the underside. We can probably safely assume that the alloy they cast with is the same. That means the difference is potentially in the bushings and machining tolerance, or not. I'm impressed with the PRW rockers. I got these for $150 on Amazon on closeout, usually $400+. I think the SM version is priced pretty aggressively against the PRW when they aren't on sale too.
Had a nice heavy box on the porch this evening too. Now I think about all I need are some gaskets and a new water pump.