If you're checking for burned valves, the obvious check is a compression test. Judging by the last post I guess you're just asking about valve guides. A theposcope will help you pinpoint the rattling. I would try adjusting the rockers first if they're adjustable (I haven't accessed mine yet).

I know on most of the Chevorlets I've owned, rocker adjustment is a delicate balance between science and art. Overtighten and your cam lobes disappear. Undertighten and get clackety-clack noise.