I think what needs to be addressed here is why do the engines have a draft tube...or PCV.... or valve cover vented cap...etc.
It must be remembered that when an engine is running some hot combustion gas will leak by the rings.... no matter what.... particularly if the engine is worked hard and /or tired. Without a opening somewhere things are going to blow as the fumes accumulate inside the crankcase. On a well worn engine it is not unusual to see blue smoke pouring out of the bottom of the engine ( old style draft tube) almost at the same beat as the engine cylinders are firing..... sort of a chug chug chug of smoke.
Just having a small vented cap on the valve cover would probably not suffice to venting all the fumes.
The old engines used cut out slits in the valve covers do draw fresh air into the crankcase and the fumes where sucked out the draft tube as the vehicle moved forward.
Eventually manufacturers.... somewhere around the beginning of the WW II realized that in adverse driving conditions (North Africa) too much dust/abresives were sucked in the engine and greatly increased wear. Early 1940 GM military 216 were issued with the slit vented valve cover and old style vent pipe... soon to be replaced with a PCV valve, no open draft tube and a medium size oil air filter on the valve cover to allow clean the air to be sucked in the crankcase. The process was critical in making military vehicles water proof for beach landings. During landings, for short periods, they would close off the air intake on the valve cover and let pressure build up in thc crankcase pushing water out of any leak area. Immediately after landing they were told to open up the air intake to the crankcase...
The PCV... Positive Crankcase Ventilation valve... is a system connected to the vacuum side of the intake manifold and maintains a slight positive (vacuum) sucking of the crankcase fumes back into the combustion chamber.....
Later on (1955+), the PCV was refined and the valve cover became vented by a large 1 inch rubber tube that drew fresh air by being connected on the clean side of the engine air filter.
I would not advise running your 235 with out a properly connected PCV connection as you may cause oil leaks, damage gaskets and probably build up sludge faster than normal. You will still need a vented valve cover cap.. the ones with the metal fiber inside to trap dust..... the metal fiber inside the cap should be washed in gasoline and oiled with fresh engine oil at every oil change.
From your picture, you still have the PCV on the engine.... take it apart and clean out carbon/oil that may have build up....(carb cleaner solution works good) don't break it or loose as they are hard to find. The early steel type as pictured will unscrew apart for cleaning.... watch the sping and plunger inside.... you may want to replace the rubber hose with a nice clean 3/8 steel brake line right up to the manifold connection using a simple flare.
If you do happen to need a new one.... the only source I know of is from the parts suppliers for old WW II Jeeps such as Peter De Bella ... they are worth about $25.00
My 5 cents worth...
Bob C.
