When I converted my 37 Chevy p/u to tube shocks I used a kit that had plates that needed to be welded in the frame,well I had to reweld them a couple times so its time to improve on it and had been suggested to make a crossmember to mount the shocks so would there be a universal crossmember shock mount available.
I used thick wall 2x2 and made my own. Make sure sure you are your shocks are to long and bottoming out before your suspension is, shouldn’t be that much force to brake welds.
I am guessing that the best reason for a separate new crossmember is to make sure the mounting brackets are being welded to clean metal with good quality welds, not to rusty 85 year old frame material that resulted in cheezy porous and weak welds. If the original shock brackets were reasonably designed with adequate weld bead length and placement they should not have failed if they were welded to clean parent metal.
I don't know what it's original purpose was but I have a length of heavy wall 1 or 1-1/4 square tubing as a cross member to hold the shock mounts on the back of my 48. That's been on there since 1989. The tubing does have probably 1/4 inch walls.