Solution found: it is standard aluminium extrusion available at Aluminium Trading Centre).
https://www.aluminiumtc.com.au/store...3-id-14mm-152/
Bolts (3 or 4 or even more) could be M6, 120mm long (they could also be threaded rods (Bunnings), with nuts&washers at each end).
The structure can be reinforceda bit further by number of countersink screws (M4~M5, shown on the second picture).
The whole thing will cost me around $20... ($15 for 1.6m channel, $5 for screws) with some leftovers for another project (I will have to use ~0.5m or a bit more).
I even do not need to shorten the bar, I can leave it as it is (while waiting for better solution.... but we all know that temporary solutions usualy last the longest time...)