Jeff,
I would make darn sure that the draft tube is Clean. In fact if the truck is old and setting around for a while I would remove the draft tube and soak it in solvent. I am restoring a 1935 with a 1937 216 engine that I bought. It had a lot of miles and sat around for a few years. When I started rebuilding the engine I found that the draft tube was filled with dirt. What you have is an inefficient system. As you drive along, the air passing by the draft tube causes a suction which draws the air (filled with oil contamination)out of the crankcase, so you would think that no dirt could not get into the tube but it does. The intake air comes through the three slots in the top of the valve cover and is pull down through the oil return hole in the middle of the rocker arm assembly. not vary big but enough if the draft tube is working. For my truck I have purchased a new valve cover with the oil fill cap on top. It still has the three slots for intake air. I removed the draft tube and and fitted the hole with a freeze plug and a 3\8 tube fitting. One side of the tube goes to a PCV valve and from there to the intake manifold. I have not tried it yet since I am a long way from start-up, just engine mounted on frame, but I think that it will provide a nice positive way to keep the contaminates out of the engine. Someone in this forum said froth was coming out of the draft tube and they were talking about moisture. I think that there is a large build up of contaminates causing it and the tube is probably blocked. Don't take a chance! Make sure that it is clean.
