Be waring of the drop down jockey wheels. I have seen a few photos and one in person that have failed and not with nice results.
Simplest action maybe to just heli coil your existing clamp?
If welding as
@bigcol suggested you need to know what your doing, and don't leave any wires in the drawbar. Follow guidelines closely cause you can indeed weaken a drawbar.
The best thing about a central jockey wheel is they seem to be stronger against pushing the van sideways as your not exerting force on the opening part of the clamp. On ours going across meant I had to remove Jayco's 25mm cross bar and welding to the other side and I also had to disconnect all the gaggle of wires and pull then from the a frame as well as still offset it to miss the brake lines. So bought a HD clamp and new offset bracket from Preston chassis same as you are starting to see on all the other vans and welded it to the inside.
Edit no I didn't wels across the chassis top I folded them further from the 45deg to nearly 90deg and tacked them to to the other side.