Boy, I just about fell onto page 3. No excuses, just too many 'other things' to do; perhaps I am not single-minded enough. Maybe I should have spent less time on the computer ...
Here is some stuff 'mocked-up.' Not exceptional progress, but at least I'm making swarf and filings again.
I didn't quite follow Modernbeat's suggested approach to roll bar support (well, not at all?) and instead developed a mixed arrangement of an 18ga fabricated angle combined with a 1x1 RHS. The photos show pre (RHS) and post (LHS) pictures, albeit with magnets holding it together rather than weld metal.
I am using Speedway four-bar ends (instead of Heims) and swaged bars for a three-link system. The four-bar ends work very well with 1 3/4x1 3/4 .100 wall tube for brackets. Only minor shimming will be required. I have mocked up a forward support for the third link based on 1 3/4 RHS supported by 1x1 RHS transverses. I am a little uncomfortable with clearance to the rear u-joint flange at the moment, so I may raise the whole arrangement, which will require more swarf and filing making. I have worked out the clearances - as someone else said, clearance is clearance, but the fear of a u-joint flange whacking solid structure on full bump gives me the willies!
The sides of the tunnel are plated in 16ga. steel. Any thoughts on whether I should have more stiffening for the forward bracket? Locomod uses diagonals, but then again he has an 'open' tunnel structure.
I'm going away this coming week, but hope to come to a decision on the three-link when I return and do some welding again. Welding the forward third link bracket into the tunnel is going to be 'interesting'.