Retune my entire carb after installing new heads?

In your initial post you said that the afr leaned out one full ratio across the board, So if it was my carb the first thing I would do is up the main jets 2 sizes all the way around ( if I remember right 4 jet sizes is one afr ratio). While you have the metering blocks off for jetting, up your idle feed restrictions(idle jets) by .002, see where your afr is. Then keep going up in in these small increments till you get the afr back where it was before the head change and yes you will most likely be tuning every circuit to get the carb perfect. You opened up a large restriction in the air flow in that 451 when you went to the higher flowing heads, so now it needs more fuel for all that extra air. At least that my take on the problem.