I have a ZZ4 in a '68. Needless to say, this is not a combination that shows up in any application book. So which PCV valve is a boy to use? Do the part numbers actually have some significance?

Ed

Yes, it does make a difference. I would get a valve for a high performance engine like a '69 350 or a 302. You could also try an early 70s LT1 350 valve. The springs in the valves are different, causing the valves to open/close at different vacuum levels.

I agree with Gene. Use the book at the parts store to find one of the higher HP engine from '69 or '70. You'll find the wrong one will effect idle quality as the pvc system is a controlled vacuum leak.