The valve train issues for a sbc at Ultra High RPMs are (1) Valve spring pressures, (2) Push rods and (3) Cam flex.
(1) High valve spring pressures are unavoidable in a high rpm, high lift, high flow, 2 valves per cylinder engine due to the weight of the large valves.
Ever notice that the High Rev exotics use 4 valves per cylinder? One of the reasons is a smaller valve weighs less and requires less spring pressure to prevent valve float.
Higher spring pressures also place more stress on the rest of the valve train.
(2) Push rods experience NASTY harmonics above 10,000 rpms and can literally shatter/explode!
(3) Cam flex is BAD and directly related to shaft diameter, valve lift, spring pressure and RPM. In short, the more spring pressure and rpm, the more cam flex is experienced!
The BEST solution would be the use a 4 valves per cylinder head capable of high rpm.
Like this for example, http://www.araoengineering.com/
Unfortunately this would NOT be an inexpensive option.