That swap can getcha into a lot of time and trouble.. I think I would pull the offending head and lap a new valve in place (leaving everything else alone) and reinstall it! Then If I wanted an engine with the 4.0 head I'd be building one in my shop to install the complete engine in the future.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist