[sierra4x4]

For the application that you have I would say go with the 366 heads but make sure that you do get the closed chamber ones. I just built a 454 for my k20 and I used 366 heads and put 454 valves in them(206int,1.72ex) so that the valves arn't shrouded as bad as they are with larger valves. The heads that I used had 235cc intake ports with 99cc combustion chambers. All I did was a little bit of bowl blending. When picking heads for my engine I found peanut ports to have 205cc intake ports and 781's had around 265cc ports. So I chose the 366 heads becouse in a 4x4 I wanted to have lots of low end torque and I figured the smaller ports would help with that and yet they still make excellent mid range power all while increasing the compression. I am very happy with the combination it makes awsome low end torque and will pull to past 5500rpm. I'm sure 781's will make more top end power but you will loose low end torque with the larger ports and lower compression.