well with such small duration i doubt the shims will be affected, though to run 9mm lift i'd advise better valve springs, and retainers to take the extra strain from the pressure that would be created by heavier springs.
as for the duration ive heard the same thing, that it is safe to use upto the 260-270 degree mark on the inlet side, i have even seen a hks built motor with an adjustable variable inlet pulley. from memory though 260 degree isnt much of an increase over standard.
the specs i heard of, were 26* on the inlet with standard pulley, and 28* with adj cam pulley on exhaust.
dude u wont know what will work till u try it, theres is not enough support for blacktop 20vs in aus, just get a degree wheel and have a play don't have to worry about destroying valves in the process then