I chopped up an old 13mm ring/open ended spanner and welded in a nice bit of 3mm stainless flat to extend the daylights out of that spanner....
Hmm... 13mm spanner on a 12.7mm nut, goes on easier in a confined space. Good thinking Kingy!
I made the tool as per instructions, except didn't have any stainless flat for the handle, so used tube instead. I will try it out on 1434 on Saturday. I just went to try it out on 1140, but it has the rear beam nuts welded to rectangular washers, so no spanner needed.
Checked the main beam bolts on 1140; nuts were done up tight but bolts were loose as in the holes, as nuts had run out of thread. Will now cut a bit more thread on the bolts.
Fortunately I don't have Popeye forearms, so didn't get stuck in the holes, but a bit of swearing nevertheless.