@Vikz808 ,
Sealed Power, Mahle, Clevite and a few more offer replacement pistons/ring sets, gaskets/seals, lifters/rockers and bearings for the OHV 4.0l.
I am faulted and have never bought a kit but I can recommend speaking with a reputable local machinist. They get parts at "Jobber" price and have the option to pass on the savings.
My local machinist goes through the local Parts Warehouse; he tells them what he is building and let's them recommend the parts based on the build's requirements. Despite this, I have always sourced my own choice in pistons for reasons specific.