350 is great for a performance engine build. The power is made from the package. Use parts that are made to work together and are proven.
Melling is the performer cam 420/442 lift , correct. I would use the performer intake. Not the RPm intake unless you have a lot of gear 4.10+ . Stay away from most single plane manifolds on the street.
NA hydraulic cammed, 9 ish to 1 engines I have built are good for .75-.85 power per inch. A sbc making 300hp is a fast engine with a good amount of power.
Lift should clear the pistons. Do not really worry about that till over .450 lift.
Not sure about rejeting , but a 600 holley at baseline should be pretty close. Better than a 770 in a heavy longbed.