Helped with a booster removal only once on a 65 and the bottom nuts are a pain to get off. There’s no secret, at least that I know of. It was trial and error with sockets, universal joints, extensions, and box end wrenches. We tried working from the top and bottom eventually mostly from the top. The wrench for the inside nut was lined up in the area of the voltage regulator and the wiper motor was removed to get at the outside nut. There was not a lot of room to swing the wrench. All I can suggest is try a bunch of different wrench combinations until one of them hopefully fits and allows for some movement. FYI, once the booster is loosened, the master can be removed and gently moved forward without disconnecting the brake lines as there is usually enough slack in the lines. Also, since the replacement booster is not “stock” I would verify that the current master will bolt on. If not, they usually give a good deal on booster/master combos.