PVC valve is ONLY to keep a carb backfire in the carb or intake from blowing into your crank case/valve cover.
The jegs kits are crap, but I put mine together using a 4 inch nipple from Home Depot 1.24, and two Pinto EGR valves from NAPA, total cost 15 buck I think. Already had the breathers, but will probably go with the screw ins on this build for peace of mind.
Catch can is only that, it doesnt do anything but catch blow by. Where as a positive evac is actively removing pressure from your crank case, that causes pressue and misting inside the eng, robbing horsepower. At idel around town, not to big an issue, and ring blow by is not that bad unless your eng is junk.
When you put your foot into it, and get on the big end of the track, you dont want oil blowing off your valve covers etc when your pumping all that press into your crankcase from the rings.
Thats why the header evac works well on drag cars, unless you can afford the pump. The electric pumps wont keep up with the increased crank case press on the big end.