I went through a couple of references and googled the net. It seems that the 42-39408 and the 42-39713 were two different planes. The 42-39408 was the Northrop P-61B-2-NO and the 42-39713 was the Northrop P-61B-15-NO. I haven't found any pic of the 713 kite. However it seems that the serial can be seen in the offered as an oil painting and then as an image with sign.
The shots I could find, seem to show the 42-39408 aircraft with the art on the starboard. Also it is almost sure the plane didn't have the art on the port side. I did some searching and grabbed these clips. I would say it is the 42-39408. The lack of the art at the port side of the fuselage can be seen clearly. The idea ( no arts on the port side ) is suggested by the B&W pic of the 548th NFS P-61s attached here below. These clip shots indicate the red spinners and back engine cowlings
But these two may suggest that there was the black colour applied on the parts. Unfortunately the second pic is of quite poor quality and it might have been the red colour too.