The only good solution is to return them. Have a local welder make you a set. No big deal. I'd complete and mount the side pipes with flange first. Then attach the two unwelded flanges (two per side) (that will be welded to make your headers), i.e, the flange that will go on the head to the head and the flange that will go on the side pipe flange to the flange on the side pipe. I'd assume with a 351 would would use 1 3/4" pipe. The loose pipe would have various bends that the welder would then cut and fit as needed. As the pieces are fitted to the flanges, the welder would tac it all together, then remove the bolts used to hold in place, remove the tac'ed headers, complete the welds, have ceramic coated and bolt back in place. The picture you have can be used by the welder as a template. I attached a few picts of my recently built headers and side pipes on my build site.
My build link
http://www.uniquecobra.com/forums/forumdisplay.php?f=68 then click the "exterior" thread for the headers.
In addition, under my "Links" thread you see where you can buy your header parts, i.e, flanges, pipe, etc.
good luck, Mark