How are you going to keep the engine for puking oil as you drive?
That canister is an oil air separator. I prevents oil from being sucked into the engine from manifold vacuum with that canister used from 1963 through '68. In '69 the factory put two small ineffective (as seen inside the air cleaner by the presence of oil) in between the valve springs hanging from beneath the valve cover. If you use those valve covers you need a filtered air source to allow air into the motor to allow a vacuum to remove fumes.
If you leave the hole open you will get dirt into your engine as oil comes out, as air moves into and out of your motor with each piston stroke.