The GEN 4 computer is far more advanced than the 3800's or even a P01 or P59 computer. Just changing the MAF settings for running E85 is not correct. Either install a ethanol content sensor or run ONLY E85 with no mixing. There is no inbetweens. You'll have to start tuning in lambda if you wish to make the switch because tuning in AFR is no longer going to work for you.
Stock plugs work, many switch to like a TR55 or similar plug.
I think you need to drive the car and actually see where the engine runs at for full throttle so you can see where they run for timing. That LS4 will never see over .85-.90 cylinder volume without boost. You'll be in the .60 to .75 for the most part and that timing is in the 20's. They also use spark correction tables to add timing in certain parts of the power band.
