i didnt have the problem you mentioned, and we both have nearly exactly the same engine, 5K, 3K bigport head, Dished pistons and except for the cam profile, porting and dual valve springs its basically the same.
i'd be pointing to the dual valve springs as well.....i've never hit any valve bounce from my engine (single valve springs) and its been in the car for over a year now with little problems. only problem i had is now fixed and that was the stem seals.
my engine also frequently hits at least 7500rpm.....i've had it to 8200 with no problems.