Ive had very good luck with howell fuel injection http://howellefi.com/
They use factory (gm) colors and connectors and components, their customer service is incredible. Ive been involved in a number of projects over the years with people using the other peoples harness and I will only use them.
My last project was a 2004 astro van 4.3 and 4l60 auto into a 1984 toyota pu. It had to pass Ca emissions when we were done. They didn't sell a harness and pcm for our application so they made one to order. After install we found out there was something in the pcm programming we needed changed. They sent us another pcm with return shipping free of charge.