I believe I heard that they are aluminum against the shaft or bushed. But even with a bushing, the "body" strength may be even stronger than regular HS rockers with the caged needle/roller bearings because the body may not be machined as much to install them. (If they use the same body.)

I also noticed that the shafts are "hard chromed" which may indicate that they are comparable to what Mopar & Crane sell for their ductile iron and/or aluminum rockers. The regular Harland Sharp rockers are advertised as using "heat treated, heavy wall rocker shafts."

May have to call Mancini for a wall thickness comparison as well as what their assemblies are rated at/recommended for.