i am no expert, and there are guys here that know way more than me on this subject, but........
i would check the math on the costs of doing those heads, parts and labor.
unless you are able to do some of the work yourself (porting/bowl blending for new larger valves)
also the cost of the springs and other pieces for the cam etc.
you might find it with be worth the couple extra bucks and just buy new heads
it all adds up quick
i'm building a set of 781's and if i was to do it over, i'd just sell them
you may be able to find a set that will work better with your flat top pistons