Well a 406 is a whole nother deal. 4F3 is a date code of 64/Jun/3rd. The 406 was a 62 1/2 to 63 1/2 only deal till the 427 first came out in late 63. But there were a number of service blocks which had very THICK cyl walls. Basicly the 406 service blocks can go to 4.23 std 427. Is there a casting number on the block? Also look for a "HP" and the block should be a solid lifter style with a oil pressure releif valve above the rear cam plug. Is the crank a 406 crank also then? If the rods are early 427 they might be C3AE-3. Look on the crank for a casting number also or any letter/number like IU, IUB, 2U, 3U etc.. Ford used full casting numbers then went to a simpler ID later on cranks. All these things will really help ID what you have. G.