Pushrod length is best determined once the heads are on the engine. In most instances, a pushrod with an effective length of 8.000” will get you in the ball park though. Just insure that the pushrods you use have a cup large enough to fully support the ball on the end of the adjuster screw. Too small a cup will eventually cause a pushrod failure.
With only a 0.020” cut on the heads and 0.020” cut on the decks, there should be no intake manifold fit issues if using composition head gaskets.