[Bill Baer]

I haven't seen a pair of Merlin aluminum heads but 800 hp from a 555 is a little on the weak side they usually are in the 900-1000 hp range with conventional heads I have utlized brodex and BMF heads the cnc ported BMF heads on my 540 made 890hp on the dyno and on my engine builders 567 they were over 1000 hp on one dominator. Granted there are a lot of factors involved in building horsepower but one of the biggest factors is the ability of the heads to provide the correct air flow, velocity, swirl and air fuel mixture homogenization.
But as I mentioned there are alot of factors affecting horsepower perhaps with a cam change or more compression etcetera the melins could produce simular results. In my experience the BMF heads work well.

Just my .02 worth.