A few days late, but that isn't a 429. It's a Ford FE, 390/427/428 series of engines (and a host of other displacements). Between the 2 center spark plugs there will be a casting number for the head, that wont determine size but could narrow some stuff down. Also, look along the block right above the oil pan rail, if you see three bolts on each side that go into the block about where you think the main caps might be that would be good as it would most likely be a 427. Else pulling a head is about the only way to determine the actual engine size.