The concept is a good one and obviously working well. A similar concept is used in V8 Supercars, even though using a 4 link they still run a cushion in the top arm. This is a bump rubber, or a set of 'Belville' washers (cone shaped) stacked up to form a spring, on a slide. You aren't looking for much movement, 3 to 5mm at most but it is enough to bring back the compliance , loose the bind and put the power to the ground.

You must have some really good shocks as those springs would be as soft as Mother Teresa's heart, & if axle breakages are becoming a problem, then perhaps periodic axle inspection will need to be something that needs toi be tacked onto the race-prep checklist.

Axles rarely just break, but instead they most commonly show signs of twisting at the spline first, then they 'eventually' break, so a couple of spare axles & an occasional inspection might save the day.

I have noticed that cars with locked diffs are more prone to this & I suspect that this is due to the fact than in uneven traction conditions, just one axle is doing all the work, carying the whole torque load, & the loading from a high performance engine is enough to do the damage.

Nice work - what size rose joints did you use?

I just tried this setup at an autocross, it must work in giving better traction because I broke another axel.?