Converting to DI is a BIG project! If you are going for it, you may just as well put in someting bigger/stronger (like LS4 or Nortstar) . Also, I do not trust "rebuilt motors" unless and know who did it. There are SO MANY ways to screwup engine assembly, that it is just not worth the risk.

I would take a 100-120k miles factory built motor over an "unknown rebuilt" any day!