i love how this went from: do i need to pull the clutch fork and when do i install the z-bar? to i'm just gonna go with x instead of the advice i came seeking. but i digress...
with the headers in place it's going to be extra tricky. also, i don't know what your situation is but you're going to need a cherry picker that gets up there a good ways, like WAY more than you think it needs to. and you'll need a friend, possibly two, to manage the wily business of the trans tailshaft-- getting it over the nose/rad and keeping it up off the floor and directing the motor into place.
on getting the trans into the bell and engaging the pilot, it's not like you're dropping a quarter in a shot glass or some bar trick. a floor jack, steady hands and using common sense: ie not forcing anything, or slamming it together, is all it takes.
if you're really that concerned about it, just drop the K and attach the motor and trans assembly and install it as a complete unit from the underside. you can even put the headers on in that case. you'll still need to put the Z on after everything is in place though.