Just bought a 360

I just bought a 360 complete engine today casting number on the side is 53006921 date code on the other side is 11/7/90. Now whats odd is this motor has a roller cam in it. I knew roller cam could be installed in these motors which is why i was buyin it but i didn't think the 91 dodge vans which i came out of had roller cams in them that year. Was this roller cam installed from the factory or is this the doing of aftermarket work.