They will work with stock heads. The valve old stock valvesprings can give way and you can float valves. I have personally bent valves with an e-cam, IDK the rpms cause it was a carbed car, with no rev limiter, and I have also had 130,000 mile springs with an F-cam hit the fuel cutoff and not float.well i dont have the money to replace my heads right now since im getting a whole new block, and i want a new cam put in since everything else is going to be new, and aparently the e303 wont work with stock heads so i guess my only option is a stocker right??