Your extra frame itself fits bearings fine, it’s just the cap that’s bad right? If so maybe build one frame into a v frame with steel tubing and leave the other one alone for different riding styles or incase anything goes wrong with the v frame project. You might be able to salvage some material from a crappy bicycle. Generally I think V frames are more of a road unicycle thing versus mountain so maybe leave which ever frame fits a wider tire for muni and build the other one.