Custom Build means that we need to rebuild your core; which will require you to send us your engine first. This process is very similar to returning a core. Make sure ALL FLUIDS ARE DRAINED and everything that needs to be taken off is taken off, we have instructional videos that explain what to take off and how to prep your engine for shipping. If you can't get something off or forget something, we will do our best to make sure it is removed, cleaned and returned; however, Sunwest is not responsible for any loss or damage of extra parts. Valve covers and oil pans are the exception: if you would like us to clean these parts for you, you may leave them on the engine. We will make sure they are cleaned to our standards and return them to you with the engine. Sunwest DOES NOT REINSTALL things like valve covers, oil pans, intake or exhaust manifolds.