Does anyone know which year Ford changed the 4.2 V6 from internally balanced to externally balanced?? (or from external to internal balance)

I have just put a replacement motor into a 99 F150 - manual trans. The old motor was internally balanced - no offset weight on the front pulley or flywheel. the replacement engine has an offset weighted front pulley and flywheel. The clutch pressure plates are different and i need to know what year/s to try.


Appreciate any input. Thanks
Kiwi