what kind of condition is your intake manifold in and how well is it seated? i had a similar problem with a 302, ended up that my intake manifold had small cracks in it enough to let oil into the cylinders... the reason it only happens on startup and higher RPMs could easily have to do with your oil pump, pumping harder when its at those higher RPMs... the only way i found out that this was the problem on my engine though was that my oil pressure was slowly rising from 60psi to about 120psi in about an hour, which was because water from the radiator was leaking through those cracks as well, but its not always gonna be what happens depending on where the cracks are....

also too much chrome for my liking.... chrome brings engine temp up, and i like to keep mine as cool as possible