Long valves on W2's with .600 lift?

With a flat tappet cam, the max lift is limited by the lifter diameter and the duration.
If you push the rate too far, the profile runs off the edge of the lifter(at which point you have instant failure).

.570 lift for [email protected] is using up most of a .904 lifter.
A Howard’s .904 SFT profile in the [email protected] range would be up around .580 lift.
There might be a tad more lift available, but it won’t likely be a very reliable combo.

For the most part........ either change the rockers, run a roller, add some duration(with the same rate of lift, more duration = more lift), or learn to live with it.