I probably wouldn't have widened the deck to get closer to the fence as the wider it is it's harder to mow around trees .
You can widen the deck if need be but I would just mount the deck more to one side.
I can't see it not moving around even when welding the u bolts onto the axle tubes as it's fitted like a tractor slasher but a small compact Tractor is 2 to 4 tonnes and it still uses at least one wheel at the back of the deck , this bike being a lot lighter than a tractor will move the deck all over the place, especially when turning in my opinion.
It's getting there shouldn't take too much more work , I guess weld the bolts and try it but if it's still moving it's just a little more work to fix.
