I'd go for the merlin heads, they are going to flow more than your 781's even with the bowl blend and bigger valves. And they also come with new springs, retainers, etc., which you are going to have to buy also. I believe the Merlin heads flow about 280cfm out of the box, so with a bowl blend and minor pocket port work you will be over 300cfm. And for a couple hundred $ more I think it's well worth it.