If it is the heavy polyester twill or doubleknit, you will definitely want to tie it, as that is both the easiest way to do it and also the way most of the ones made in that era were done. I'm guessing it is most likely fairly large squares or rectangles, which could be tied either at the intersections or the center of the patches. It is probably machine stitched. You could even just find some of the corresponding twill or doubleknit and use that for the backing, no batting needed.
These are awesome camping quilts as they wear like iron and can just be tossed in the washer and dryer (low temp for dryer).