The mid-corner understeer your experiencing is most likely from those dreaded KYB's. The car is transitioning too quickly due to being under sprung/dampened and is rebounding ans unloading the outside tire causing it too loose traction mid-corner. Throw the SPAX shocks and the 1.03-1.12 torsions on the car and see how if feels.

A car can only go around a corner as fast as the front tires will allow, so work on the front first with the budget you have and get it working right. You can band-aid the rear leafs for practically nothing by adding a leaf or 2 to your existing ones and then modifying the front hanger/shackles or adding a block to get the desired ride height.

Also, make sure you have an aggressive enough front alignment. After you've done the torsions and shocks you will need a little help since the sway bars are a little on the soft side. I would run:

-1.5* camber or more, I run -2* on my daily driver
As much positive caster as you can get keeping it the same side to side
and Zero toe