I did the TBI swap into my '74, and it seems to run great (I finished the swap a couple of days before taking it to Vintage air, so it hasn't been driven much). I used the harness from
www.fuelinjectionconnection.com as I didn't want to take a chance on 25 year old wiring. The harness was $245, and it was stand alone. There are just a few wires to hook up, and then swapping out fuel lines.
There is a lot of good info on
www.binderplanet.com also. A lot of people on there are adapting the GM TBI for use on their IH engines, so there is a lot of info on how to make it work, cleaning up the harness, etc.