If you are using a LS head you are going to be limited to about 325-350whp. Your block can handle that no problem. As for injectors I would not go any smaller then a 550cc. As long as you are getting tuned you can use anything from 550cc to 1000cc. As for turbos if you want to use a T28 sized turbo you are going to have to run one of the bigger ones (GT2871r) to make the 300+whp. Also, remember that if you run an internal wastegate turbo it makes it a little more difficult to fit with a/c.