Rebuild help

[nitrostang66]

I just have bought World products 351w assembled heads to replace the stock heads on my 69 302 block. I have not had to do this type of rebuild before and don't want to mess it up. I have the bolts for the build, gaskets, and am going to buy new rods, roller rockers, and possibly a new manifold. This is my set up, a rebuilt block with around 3000 miles on it. The piston walls are fairly clean,except for dust. I have msd, a stock cam, and a 600 holley. The tranny is a c-4 with a b&m kit as well as a 2500 stahl. I am running stock gears in the back. I have an Eldenbrock RPM manifold. The shop where I bought the heads suggested that I take off the rpm manifold, and just go with the proformer manifold. I am also going to buy a new set of headers. These are involved questions, but please help me out. 1 For power what is the answer with headers and the manifold?

2 I have access to all tools, but what is important in the rebuilt, having not done this type before? 3 what would help my set-up? Since I didn't say before it is a 66 coupe, and thanks for the help, just have too much money in to mess it up.