Speartech did my 78z LS1 harness and PCM reprogram in 2006. Everything is flawless. I even called him a few years AFTER ....like this Spring when I was putting in an AAW Hwy 22 wiring harness and he still helped me. So he's GREAT for support and quality.
I am possibly doing another retrofit and might consider doing the mods myself this time not just to save the money, but to gain the experience.
However, if I fail, I'll be calling Speartech to do it.