Shane--
When a pcv is added, the downdraft tube is typically removed and replaced with a filter to draw clean air into the engine and crankcase fumes are drawn out usually thru the valve cover to the intake manifold where they are burned and exhaused.
The first time I became aware of it was when I was a kid haulin hay. My little AD jimmi did fine be driven to school and around town but when it spent all day crawling around a hayfield it would turn a crankcase full of oil to sludge literally in a day--speed was too slow to allow the draft tube to evacuate crankcase blowby and of course the rings on these engines never were much and were typically worn out anyway. Back then--in the mid sixties--they sold what were called ventilation valves. Run a tube from valve cover or valve cap to intake manifold with ventilation valve in line--and put a filter in the draft tube bung. I've seen em run both ways--exhaust to intake or exhaust to fuel pump. Lotta folks also ran exhaust to air filter--but I never wanted to run that nasty crap thru a carb.
I suppose as long as ur truck is always run at speed--draft tube will get u by but pcv will keep ur oil cleaner--my 2 cents.
