To clarify/confirm, the point I was planning to mount to is the framework not the axle tube: -
Since the BAL jacks I have don't have a flat surface covering the top, and instead just have two flanges, I was considering mounting a 16 gauge steel plate to the top of the jacks, and then securing that to the mounting point in the photo with two U-bolts (U bolts would hook over the framework shown, and secure through holes in the steel plate using nylock nuts and washers.
Do you think that sounds workable ?
I'm hesitant to drill holes into that framework beam, and if I can avoid having to get something fabricated/welded by a metal shop then it saves me time and money and hassle.
Even I can manage to cut, and drill some holes in, and paint some 16 gauge cold-rolled steel sheet myself