I am in the unfortunate predicament of needing to replace the head assbly of my 07' 450- Cam journal on intake cam is out of round & bearings are suspect on cam. I see on ebay a hefty difference in price between year designations. I would suspect they are not interchangeable- but thought it best to ask here before assuming. Is the earlier style usable? - and if so 1)what are the differences in the earlier vs. the later models and 2)what else needs to be changed to make it work.