426 blocks are not symetrical.the bore space is but the ports are not which is why you see the pushrod clearance differences cylinder to cylinder. 1 and 5 are the same 3 and 7 are the same as each other, but different from 1 and 5. Normal, but you change that often in a race motor to symetrical port location. Better to start without lifter bores in the block if you're going down that road too