the way ive set pinion angle before is slap the perches on there put it under the truck, crank down on the u bolts, then with the weight on the truck put a jack under the pinion and jack it up to where it needs to be.
in your case its too late for that. id cut grind and do it right then re weld. no sense in spending all that time just to half ass it in the end, ya know?
Hunter