Some more pictures from today's lunchtime walk which included a swing past the tractor shed... Note that this is not an easy weldment and it was a somewhat time-consuming job to get this on the tractor as it all just fit. You would likely be better off not making a one-piece weldment. You might combine it with a mounting rack for suitable weights; these little units are sturdy enough but lacking in ... gravitas.
There was a program (at least here in the US) where Kubota dealers would offer ROPS for tractors originally offered/shipped w/o them at very reasonable prices; I used this and I doubt the $250 or so I paid would have covered shipping, let alone fabrication. You might see if this is active in Ireland; it may be limited to the Litigious States of America.
As you can see, the ROPS picks up 6 bolts into the PTO drive area, and two on each side on the differential housing.
The ROPS itself is made from 2" (50mm) square tubing perhaps 3/16" thick
; I'd guess the mounting plates are 5/8" thick.