Auto-X / Roadrace rear suspension 1969 Valiant

As for the other stuff, if you mounted the springs splayed you'd have to mount the sliders so they were at the same angle as the springs to prevent any binding. So parallel to the springs and not the frame rails if you mount the springs at an angle.

As far as keeping the rear end from going left and right, there's a few things. First is just the design, the flatter the springs are the less likely they are to deflect laterally. Hence the "zero arch" spring design from Ma Mopar. Then there's a few other things, like the spring sliders. The spring sliders allow for less side to side movement than the shackles would. And if you did composite mono-leafs, they would tend to flex less laterally than a multi-leaf spring because you won't have the leafs sliding around. So just that would help improve that. But the panhard bar should help a lot too, you just have to make sure you're mounting it properly so you're not inducing more binding with it too. To me the panhard bar is something you might not add right out of the gate, like if you determine when you're actually racing that the rear end is still moving around too much you could add it. But I think that will depend a lot on what you're doing, what tires you're running and at what tracks.

Yeah I've looked into the splined sway bars before, at some point I may get into doing that. But I'm pretty happy with my Hellwig bars for now, at least on the street. I have a lot of geometry and suspension math calculations to do to really blueprint my current set up before I get too crazy with things like splined sway bars.

I'd definitely ask some questions about the spring rate ratings from the companies and how they compare. In general I think 120-130 lb/in is a pretty good ballpark, but composite mono-leafs will have a different reaction time than a traditional multi-leaf so the rates might be a little different too. I haven't run them myself but I've heard it's not necessarily a 1:1 deal, like if you thought your current traditional leafs were right and they were 130 lb/in it still might not mean buying 130 lb/in monoleafs. But that could even vary one company to another.