Could pushrod length be wrong?
That doesn't really matter because you're using adjustable rockers.
Look at the undersides of the valve cover to see if any of the rockers are hitting the valve cover.
I know the motorsport valve covers are supposed to clear larger rocker arms, but those look HUGE!
Just a few thoughts..
-In your article you said that you went another 3/4 of a trun after the rocker arm touches the end of the pushrod (or something like that). While that sometimes works a better way is to jiggle the pushrod up and down when tightening the rocker arm nut so you an actually feel and hear when there's contact between them. It also verifies that the pushrod is fully seated in the lifter (sometimes they can hang up "off-center" on the top of the lifter).
-Your article only applies to older SBF's, and newer ones that are using aftermarket adjustable rocker arms (stock was positive stop rocker arms).
-Never use pencil to mark off the inside of the distributor cap! (the lead can cause the spark to arc)
-Instead of rotating the crank two full revolutions to go through the timing order you can do them all while only rotating the crank within 270* (there are a few books that have a good picture on how to do this... just a little faster)
-Instead of marking the cap where the plug fires you should go from where the #1 cylinder is at TDC on it's compression stroke, and mark the others from there. (With the timing advanced 10* or so your distributor cap is also 10* off as well so where the plug fires is NOT where the cyls. will be at TDC)
All things considered it's a good article! :beer
-Paul