The 99838-12 can be shimed to work. They do suck as they dont fit for one and they will lose thier tension in a street car in just a few short months. The K-750s set at 125-130 on the seat will last for years. They are drop on but must check installed height. They will work with the stock retainer. Been down this road before dont waste your time calling tech lines as they dont have a clue. 110 on the seat is all good until you add in boost and a few street miles then it is just not enough spring.