It's going to be very, very, VERY difficult to get a metering rod style carburetor to run well with that big of a camshaft.......without a LOT of tuning. The low vacuum signal reeks havoc on metering rods at idle, because it causes them to "bounce" which results in EXACTLY what you are experiencing. I have no doubt that's what's going on. Find a friend with a known good Holley and try it.
