Get an adjustable length pushrod checker so that you get your valvetrain geometry correct. I bought the one from Comp for $20. Well worth it IMO. Every engine is different, as are every set of heads. You're spending a lot of money on parts and machine work, get the valvetrain right so you don't wear out the guides right away.
What roller rockers are you going to use? I have a 302 with GT-40 heads with the 1:7 crane rockers. I was able to use standard length pushrods. You however are probably running flat tappet lifts and not rollers.
Standard Ford rockers for now. The pushrods I believe will work are the ones for the 5.0, pre-roller cam (1982 or so). I'll get an adjustable pushrod to make sure, though - I can't say for sure if the heads have been milled.