I would not suggest getting larger brass balls (I know, that just doesn't sound right) but instead, get the same size as original because of the pocket they sit in. I also used 1/4" SS bolts with Nylock nuts. This might be a good time to refit the door to it's proper position. Bolers were/are notorious for door sag.
I did this on my 13' Boler
by removing the hinges from the door, filled the hinge bolt holes with epoxy and re-drilled new holes at the correct location so the door sits in the proper position. An added bonus after the mod was that the latch bolt now lines up with the strike plate. I also replaced the door weatherstrip with a newer style to complete the modification.