With regards to the diagonal bar that sits under the live axle (back corner of car to the tranny tunnel) - should there be one on each side?
Pat...

I think there should be, bit late now though!

I've now welded one in just in case...
Pat...

It's only to reinforce the side the panhard rod is fastened to. Save the weight and leave the other side out.

The only real purpose of the diagonal is to take the transverse loads from the panhard rod, if anything rather than add an equivalent to the right side it would be more beneficial to find a way to brace the panhard rod mounting in an additional axis