12:05 Garage- ’70 Duster build

I messed with it but not with as much precision as this time and it was 4" below the ground. I believe this was due to the UCA and LCA angles never intersecting. I don't quite understand the math behind that. Picture the LCA near level and the UCA pointing to the sky.

Not sure I have it right but here is how I think about it.

The way I picture it is, they upper and lower lines either intersect opposite of the CL of the car from the tires, or pass through the CL of the car and intersect. If the lines intersect opposite the CL of the car, and then you draw a line from that intersection to the CL of the car through the middle of the tire contact patch, the roll center is probably underground like your estimate with the original setup.

Another way to think about it might be that if the line from the control arm intersection passes through the tire contact patch before hitting the CL of the car, the RC is probably pretty low. Unless maybe both the inner mount elevations are above their respective BJ elevation.

Something like this?