If you dont have the $ for a 350, then only buy parts for the 305 that will later fit your 350. Like gsx said, score an old 350/th400 combo, then buy heads when you have the money. Hell if you score an LT1 with computer, then you are only a cam and exhuast from 12s. If you cant afford the 350 right now, dont worry about the point of needing AFRs yet, there will be plenty of other costs of the swap to cover first.