Ray, later GMC big trucks had a PCV setup with your configuration, partially shown here. [my 46 had it] couldn't find a pic of the filler tube side, but instead of plugging the draft tube hole, an air cleaner was used on it .... maybe some GMC owner can supply more info

Bill


Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics