This is exactly what you need to consider. Once you know what you cam numbers are you can verify whether the "assembled" portions of the heads will work with what you are planning. If it does, I would go with assembled heads. I made this mistake with the GT40P's and ended up getting into having to purchase new valve springs and the tools to install them correctly. I ended up with Twisted Wedge heads as it was more cost effective after considering the purchase of tools, parts and machine work the GT40P's were going to need for my cam.If you're sure that the valve springs that come on the assembled heads are the right ones you need for your particular cam... and that they will handle your proposed valve lift without getting into coil bind... or the retainers hitting the valve guides... and that the valves are quality pieces and not two-piece stock replacements...