A member leant me one at the NEC, some years ago, when we adjusted Dusty's door tension.
It was just an old lump of 3X2 or was it 4X3?, going across the top on the engine cover, with a bit of similar sticking up, with a V cut in it, so as to be in line with an extension socket on the end of the torsion bar. In other words it just supported the extension bar about a foot away from the socket. I think Mark ended up managing without with a few of us helping. Not something I'd fancy doing on my own. Plenty of rear windows have been smashed doing this job!
CP