well you need the special tool to do it first off---with the head on you need to make sure piston is up so the valves don't drop into the cylinder---get some extra nuts for the tool before you start---I used a wire to double check--just removed each injector and put the wire in---if I remember correctly you can do half at TDC and the other half at BDC, but you better double check that---
head off no issues--would be easier, but it's not necessary---chris