At nauseum..318 intake manifold to 340 or 360.

intake-head mismatch on a street beater is a huge red herring.

Run whatever intake you have on whatever head you have. Lots of alum intakes recommended for a 340/360 have 318 size ports.
Ede 600-650 and make sure the kickdown is set up properly as @junkyardhero mentioned. REALLY important with an auto car.