Finally got round to welding up from the piece I cut out in Jan
Just need to cap the end of the open tube
Then modified my 'development' seat to version 1.1.
Lopped off the top (might take a bit more off later)
then increased the length and decreased the slope of the 'ramp' on the bottom.
I just completed exactly the same step with the steering rack mounts as yourself. Seems very sturdy, seemed such a shame to cut the support rail.