Brad,
I'm assuming you still have a stock intake manifold on your truck? One of the problems with stock intakes is their tendency to plug up the PCV tube that pokes into the center intake runner. If that pipe is restricted, then excess pressure will build in your motor any time the rpm's get up high. On numerous engines I've had to remove that pipe and plug it from the top, and then drill and tap an extra hole in the intake right under the carb for a new fitting where the PCV gets plumbed. The early motors had that configuration from the factory; I've still got one on my original '63 292 1-bbl manifold (on a shelf though).
If there is excess pressure from whatever source, the motor is going to relieve it someplace. A vented breather cap is the easiest place to come out, so that's usually where you'll get an oil "leak".
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David
newbie #4153
