Mike, I agree with Pete that with your arrangement as shown, the two wishbones not only provide lateral location for the axle, but in combination, prevent any roll motion as well (at least to the degree that the wishbones don’t deflect due to the loads). And those rolling motion loads may create rather large loads on the bones and Heim joints. And those loads would be such that they cause bending stress in the shank of the single Heims--something they are not designed for nor intended to carry. (Bending across a threaded shank, especially in a salt environment).
When Speed Demon was building, the early photos of their arrangement alarmed me for just this reason, and I had a discussion with Steve Watt about it. One element that Speed Demon did have that doesn’t appear in yours was a monumentally stiff anti-roll bar (about 2” diameter) which would tend to share the rolling loads with the wishbones. The photos didn’t really show the A/R bar and while the anti-roll bar tends to improve things, I still consider the arrangement spooky and, for one, wouldn’t consider riding in it. Then again, it seems to be working. But in my judgement they are just “getting away with it”.