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That is a pretty radical cam for a 302. Not a street cam that's for sure. You need to resolve your timing issues first. If you have vacuum advance hook the distributor to manifold vacuum, then drop you idle back down. That will improve the idle. If no vacuum advance them you need more initial timing like was said. Something in the range of 16-18 degrees. Depending on your compression your total timing should be around 32-35 degrees, not including vacuum advance. Generally the power valve rating should be 1/2 of manifold vacuum at idle or steady cruise. So for 7 in vacuum the power valve would be 3.5. Stock Holley power valves are usually around 6.5. So you would think when you open the throttle and the vacuum drops 1/2" it would go way rich. If your power valve is too low you can have a part throttle flat spot. With Holley's sometimes the power valve restrictor jets are not right and can make it too lean or rich, but 20 is way off. So the power valve could be right but the restrictor jets are not. Summit Racing has a YouTube video on selecting the right power valve.

I say get the timing right first and then check out the power valve.