I've only done modded stock LS1and LS3 ECM's and the wiring harnesses from Speartech and Howell for my projects. Both auto and manual projects. Between my projects (8 plus my LS swaps and 6 friends LS swaps) Both have been great with after sales tech help. I came very close to using the Holley X on my 80 Camaro LS3/4L60E swap. I spoke to Speartech , Andrew70 and Howell and it really came down to my comfort level on my swap. I went with Howell. All will cost a fair bit more than some that you can buy on ebay. There is no chance I would buy an ecm and harness off ebay. I don't know much about FI Tech. They don't seem to get much love on LS1tech. Maybe because big cams and other stuff make tuning for the FI Tech needs to be done by a real tuner. I'm glad some has had good luck FI Tech.