[xj] Rear suspension competition prep

Evening all,

I’m preparing a '72 S1 XJ for mild competition. About 2 or 3 months ago
I posted a question about installation of a torque arm to stabilise the
rear cage. I got some very useful feedback - Thanks. I will implement
this mod. (My engine will be producing around 500 ft/lbs of torque and
this is likely to twist the entire rear cage around the top rubber
mounts, leading to their rapid failure, and possibly the
failure of the radius arm bushes as well).

If I nail down the cage more effectively, which I think I can do, I am
now thinking about controlling rear end bump and roll steer by better
control of rear wishbones as well. I am considering replacing the stock
radius arms with new, longer ones, that run towards the centre of the
car, and pick up the floorpan about halfway up the driveshaft, in around
the same position as the centre driveshaft u-joint mounting plate in a
stock car (my car now runs a one-peice shaft). To keep the geometry
right, (and avoid bump steer and binding) I’d have to mount the forward
ends in the same axis as the inner bottom wishbone pivot shafts.

Do these mods sound like a worthwhile improvement over stock. Anyone
have experience with high output/quick S, E or XJ’s that could drop me a
line? Would replacing the rubber cage mounts with solid mounts further
enhance ultimate handling?

Thanks for any help.

Cheers, Andrew Robertson, Cambridge, New Zealand