fender mounting tips tricks?

[c20pickup]

front fenders need to get installed! never done this before, was going to have the body man who did the work install the fenders for me, but 7 months later and no such luck. so im going to tackle the project myself! biggest concern here is chipping and scratching my paint, the body work and paint is flawless, to help with that i used a couple strips of masking tape on the door edge to prevent chipping. any tips or tricks to help me out would be great! im told that since the cab was off the frame and i bought new bushings the side to side as well as up and down alignment of the cab could be off, which i understand. i purchased a front end hardware kit along with an assortment of shims from lmc. i ran a thread chaser through the mounting holes in the cab and fender, that didnt seem to do much and the bolts still seemed to go in rather difficult. so i ran a tap through two of the holes as a trial. one being a 5/16-18 and the other being a 3/8-16, this seemed to give me a nice thread to bite onto, is this an acceptable practice after there is piant on the threads? next issue is gap alignment. i mocked up the passenger fender today with two bolt (one 3/8 on the cowl and one 5/16 through the core support) the door to fender cab is very close on the top (maybe 1/16th inch gap) and gets larger on the bottom (around 1/2 inch gap). this would lead me to believe i need to either shim up the front cab mounts or tighten down the bolts that go through the rear cab mounts. i think im off to a good start, refreshing to see my fender back on after almost four years of work. again, any tips or tricks to help prevent damaging the paint, aligning the fender or aligning the cab would be great! shoudl probably mention the passenger fender is new from gmc pauls and the driver side is original to the truck. thanks!