340 cam timing, 1.6 rockers?

longer duration cam as the valves open more before and after tdc
lift has nothing to do with it
fast acting longer cams have more open than just longer but i doubt you have that
still you should be fine
but roller 1.6 rockers are just marketed to seperate you from your money
only of like Krooser's circle track motor where he has maxed the duration are they worth it
changing cam is not tough
post up your cranking compression when you get it on the road and go from there
need more? advance your cam 4 degrees and retest= do you like it better?
get a cam 8 degrees shorter with more lift/ area
worse? go the other way and retard it (not likely)