do yourself a favor, if you plan on modding the new engine your putting it into, build it first, cam, heads, get your headers ready for the swap. its a lot easier that way.
not that, all that cant be done in the car. if its out you have all the room in the world to work in. so why not.
and a sc 3800 won't make you happy, your going to want mod if you really want to go fast, stock is like 14 to 15 sec car, not very fast.