I am trying to research all about rockers because I am interested in putting some in my 04 grand prix. Currently I am top swapped with stock gtp L32 heads. Since I have stock heads, I am only able to get away with 1.9 rockers correct? Also if I install them I would need to get heavier springs to go with it, 90# is what I believe I read. Is that all I would need? Maybe new retainers? Tuning would be needed I assume. I want to know as much as I can before I pull the trigger. Thanks in advance!