fuel injection

Do you mean multi-port injectors? If so, I don't know of any inexpensive options. Most are "roll your own" manifold mod.s (I can't access Hilborn site above). If you are happy with Throttle Body Injection, there are several options - Holley's Pro-jection (old), Commander 950, or Avenger. There are also kits made from GM TBI parts. There was no factory TBI for the big block that I know of (production ended in early 80's?).