There were a few different designs for this piece. Some were flared a great deal and others were just flared what they needed to be. Not sure what the vendors are selling. In any case, you will have to grind off the rivets. If you were willing to drive to Kansas, I would help you put the rivets back in, but grade 8 bolts will work JUST fine. I THINK the mounting holes will line up with the vendors offerings. I have some extra ones lying around if you need a more exact match, MAYBE I have what you need. If the vendors picture looks like yours, you are good to go.
A few things to think about when installing the new ones. Chances are, the holes are exactly 3/8". Take your drill bit set and grab the 3/8 one and check the new piece. Chances are it fits perfectly. Tight, but perfect. Next, Once you have ground off the rivets, check the same way. The hole should be pretty tight. You WANT as tight as possible using a grade 8 bolt. I know this is not your first rodeo, but be sure when you grind off the rivets, you don't grind too deep. Then, use a 3/8 by 24 (fine thread bolt)/nut combination. Fine thread is stronger than coarse. If I am wrong about the 3/8 size, just adjust for the size the frame is after removing the rivet. Chances are the frame will be bigger than the vendors part. The vendors part holes WILL line up just fine. Keep us posted!
McMaster-Carr or Fastenal is a good place for sourcing the bolts and nuts. I say 3/8 because Chevy used 3/8 rivets for almost every rivet on the frame. Check before you order.
