I have a 67 c10 shortbed with a LQ9 6.0L truck engine and 4l65E trans. I used a speartech harness and stock pcm reprogrammed by speartech. I have a friend whos now done 5 Ls coversions using speartech with absolutely no problems. they are competive with the other companys that do them. Miy harness is drive by wire.
You can give me a call 217-202-8038 Fred I will be glad to give you more info. I used the stock truck wiring which was in good shape and intergrated the fuse block that came with the harness, His instruction are straight forward and simple. Everythingis color coded and you get a life time reprogramming of the PCM in case you want to change shift points, tire sizes ect. John is always available for any questins you may have and he is the one who answers the phone. My friend has many thousand miles on his and I have 2,000 trouble free miles on my truck(finished and started up in May this year)