HI just fired up my zz454 crate motor i see its got a breather hole in each rocker cover ,can i just use breather vents or do i have 2 use pvc valve thanks

2 PVCs.. 1 in each rocker cover. ..and run your crankcase at a vacuum. Good for power and bad for oil leaks. (that's good for not having oil leaks!)

If you just use breathers, you won't have crankcase ventilation - just pressure relief, with hot oil mist everywhere. As a minimum, put a PCV valve in the driver's side valve cover with a hose to the carb PCV nipple, and a breather in the passenger side cover (a hose from there to the air cleaner base with a flame arrestor is better).

Evac

Evac will be no good when running mufflers. The exhaust pressure will often be higher than crankcase.
I tried using an evac set up and wondered why my dipstick was being pushed out along with plenty of oil.. ..and yes, the evac was installed in the exhaust correctly.

Evac works well with flowmaster race mufflers ,very low back pressure. Make sure check valves in headers are good....they tend to blow out after time. That will send all the pressure back into the motor and will blow oil out of every place possible.

don't screw around. GM spent a lot of money to have some very smart people engineer the PCV setup.
use it the way GM had it- the proper PCV valve in the driver side valve cover, with either a breather or fresh air tube to the air cleaner on the passenger side.