Well I do have them installed on my GT. My boy, Brian Robak did the install - since I was way too chicken to try it by myself.
From watching him do it, it was not that difficult. Time consuming? Yes. 3 hours total.
Pretty much most of the time is spent removing everything off of the car but I would say the actual rocker install only took about an hour (maybe less).
Some of the major points that needed to be removed - dog bones on front, alternator and then valve covers - the rears was where the install slowed the most.
Having an inch/pound torque wrench would be the most accurate - but using a foot/pound one and good judgement should be okay as well.
Good luck