The TBI fuel injection system used from 1987 - 1995 is usually the easiest FI to convert to an older vehicle. There are some advantages to conversion kits from companies like Howell EFI http://www.howell-efi.com
. One of the biggest advantages is the wiring harness. It's common to find junkyard TBI systems with parts of the wiring harness cut.
It's possible to get a TBI system from a junkyard and make it work, but your going to be your technical assistance department.
Personally, I'm infavor of the GM TBI system over the Holley system. The GM system is well supported with lots of aftermarket parts and sensors. There is lots of technical materials to help learn and repair the GM TBI system.