Trailer hitch / cross member design?

[yossarian19]

I've got a Mustang gas tank in my '57, which means I chopped a cross member to put it there.
I'd like to replace the cross member and I'd like to add a trailer hitch.
The back of the frame has 2x 7/16 holes and 2x 9/16 holes per side. I'm thinking to myself "two birds, one stone". I'd like to take 1/4" plate, drill it to match the holes in the frame, weld (pay to have welded, my 90a box can't be trusted here) a 4x4x1/4 box in between them & add a receiver with gussets. Bolt it in place and voila - receiver + cross member in one.
My question is does this sound safe / reasonable? The only issue I can come up with is butt welding the square tube to the plate. I don't know if that's kosher for trailering, or if I need to come up with a new design.