Hey man, I had to do the same thing while converting my grain truck, into a slammed half ton.
I used a 71-71 crossmember, cause I had one out but grab any thing for 63+ or the 73-87 will bolt in with some hole oblonging.
but for speed, and ease of install, if you are doing this with the engine still in the truck. stay with the 63-72 half ton crossmember.
