On the older blocks there is a breather in the valley. Was this in place of a PCV valve like the later engines? Can I just put a plug in where it goes, and use valve covers with a PCV valve provision and evrything will be ok? Does the valley breather do something else I am not aware of? Thanks for your responses.

Yes you can.

Just plug it and install holed valve covers and an intake w/o an oil filler tube and plumb it for a pcv system and you will be fine.

I did my 406 this way..

Put one valve cover hole up front on the drivers side and the other back at the back on the pass. side and install a breather up front and a breather with a hose bib in the back. Then run the hose, pcv thing and more hose to the front base of the carb. (Or the back base??)...

Works fine..

pdq67

The old "snuff can" as we called them was pre PCV valves. They do about the same thing, but a PCV valve does it better.

Yes you can plug it. Thats what I have always done. My last 327 (1962 model) I done like that.

I used a frezze plug. Took out the fitting/tube, and snuff can, and tapped a frezze plug in the hole. I like to inside then upside down, so the flat part is up, and the cup of the plug is down, so the cup dont catch water or anything.

Then installed baffled hole valve covers. 1 breather in 1 cover, and 1 PCV valve (I used a valve for a 69 DZ 302 camaro) in the other cover and run a 3/8" rubber hose from valve to rear big port on my eddy. carb

If your keeping the stock intake (some folks do and I cant figure out why) then you can remove the oil fill tube and plug that hole with a frezze plug too