Shouldn't be an issue of not straight, those parts are stamped out by the thousands. What I'm wondering is if you are tightening the thumbs crews down before moving to the next. You shouldn't, this'll put torque on the mount and the last screws will not line up correctly. I'd start by loosening all the thumbs crews, back them out all the way, then apply 2-3 turns on the problem screws. Then criss-cross, 2-3 turns etc. The mount will be loose enough to just get all 4 thumbs crews started this way. Then repeat until the pump is almost tight, then switch to 1/2 turns until quite tight, then finish with 1/4 turns. My x61 is actually easier to mount than my h55 was.