There is no gun registration in PA or DE, so the rifle is now yours, or your uncles (if you want it). You can transport it unloaded and locked in your trunk from PA to DE. Call the local gun stores (X-Ring Supply) to see if they can have a look, if you don't have the experience or time to disassemble it yourself.
IANALNHIMAFRAR
"I am not a lawyer, nor have I memorized all firearms rules and regulations"