I'd wait. They should be cut from the same template, but you never know - there may be two or three templates used by the factory that have slightly different dimensions. You could work on the body but if the neck is too loose or too large, you may need a complete new kit. But if you want to progress and risk possibly wasting some time and materials, then it's your choice. It's highly likely that the new neck will fit just as well as the old one did.