Goober
if you buy the Roush motor out of a totaled Mustang, I think you should replace all bearings and seals, etc. The dynamic of a wreck will do bad things to the inside of a running motor. Flat spots on bearings, broke rings, distorted seals. I know the "yards" sell a lot of motors that are installed into vehicles and they drive away. But I think the piece of mind would be worth the cost of the rebuilt. At least the way I drive my Cobra.
Dwight