I will never use oil restrictors again.
Yes they can be used in a chevy block. They screw in the back in place of the galley plugs at the rear of the cam tunnel.
I wouldn't use them unless you have trouble with the valve covers filling up with oil and even then I would try to get it to drain back better so I didn't need them. The valve springs need oil.
jmo I know circle track guys use them and I'm no engine builder I just bolt mine together from a jegs catalog.