The inline cover without the vent slots has pro's and con's. On the pos side the lack of slots will help keep water out of your block if the cowl vent hose is cut or broken off, or if your truck is parked on a hill where the drain would drip onto the cover. The road draft tube can be capped off with a freeze plug, or a tube can be attached to the top and routed to the intake via several different routes. If this is done, you would need to seal off the road draft tube which usually was plugged up anyway. Now you need to get fresh air into the cover to replace the fumes being sucked into the intake. There are two ways to do this: provide a hose and connection to the air cleaner so the fresh air gets the benefit of the filter there or use a vented style twist-on cap on the cover. I don't like the vented cap because I have seen so many of them where the screen has dis-integrated and bits of it end up among the rockers.
There are some details of rpo options in the 47-54 assembly manual that can help you with this.
Someone should conjure up a retrofit kit for this to help these trucks keep the air cleaner. GMC and the military trucks had these set-ups on many models, they were ahead of the Chevy in this area. GMC often had a breather vent attached to the oil fill tube where the road draft tube would be otherwise located. I'm not sure if these would fit the Chevy.
