I would never use glass beads on an engine part.
Soda blast removed carbon very quickly and easily without damaging anything. Blast away on the valves and head, rockers - everything in the engine. Clean up with water. You will not believe how easy soda removes the carbon on valves, heads and pistons.
You can get a hand held gravity feed blaster from lots of sources including McMaster Carr. Or you could take the parts to someone with a blast cabinet set up for soda.
Pics of 356 engine parts before and after soda blasting.
