Re: Dart BBC heads
I have Dart Pro 1's on my 496 and I believe they have identical outside dimensions as Iron Eagles. I know for a fact they have .300" raised exh. ports. I run 2" Hooker SUper Comps on my 69 Chevelle and I only needed to dimple a tube (I think #3) to clear the steering column. Other than that, no problems. I run the Dart recommended plugs and they are all easy to get to.
As for pushrods, get the correct tool and measure it when you get to that point. Then buy the correct pushrods. If you have enough skill to change a set of heads, you can measure the pushrod length -- it's really easy. Use either the adjustable pushrod tool (looks like an actual pushrod, with adjustable length), or one of those plastic jobs that sits on the rocker stud and looks like a rocker.
Lastly, make sure you use the EXACT part number / manufacturers that Dart recommends for the head bolts. Call them if you're not sure, because they need to be the correct length. I botched this once on a small block build. I used older Bowtie heads and there was some confusion as to which special head bolt kit I needed. I paid $100 for the kit and guess what... they were too short. I found this out the hard way when I pulled a set of threads out of the block during the install and had to helicoil the block. Not a good feeling when your buttoning up a motor and the torque wrench just goes limp.