they can be just thrown in, but it is BETTER to have them fitted. I had +1mm stainless valves put in so it needed to be opened up a bit more. When my head was ported and polished, it was epoxied and flow tested too...results were amazing, but I have a high comp piston which also makes a dif. I am using the stock cam and this was taken into consideration. Total cost minus the valves was 400 bucks, valves and new springs were 250.