with head off, or lets say if for some reason you had turbo off, or perhaps as i have done swapping turbos, i like to open wastegate, you gotta go easy on this, for me, i have an ahu, so its a lever/quite thin shaft, with for me right as lever goes into turbo/wastegate it has a nice piece of the lever i can make my like about 6"adj wrench to nicely fit and easily get it to open. dont go bending or forcing, if its hard to open i consider a real good penetrant, lube. a basic one can get lever/door loose and moving, a really good one wont vaporize or just burn off. a spaceage penetrant/lube is what im referring too. may get better results. as far as having head on car, on my ahu with it on stands there is very limited space getting all the way up, in there to do this. hard enough on a lift.
as far as further adjustments to adding boost id put those plans on a hold, an engine thats running ok right now is going to be better to keep running, you may have other problems that youll find quicker as you increase adjustments, as it is that may be a warning sign.