As the car will be taken off the road in a year or so, purely to be used on track, would it be a consideration to add more castor?I would say your front caster with the mod is sufficient. If you add even more caster like I did then it will improve your second gear corners but less so your 3rd gear and no difference to your 4th.
I've always been a little put off with messing with the front ARB; as my thoughts were if I added a stiffer rear ARB to reduce understeer, would it then defeat the object to add a thicker front ARB as it would cancel out the rear ARB?What Stu and I wanted to do next was a bigger front ARB that was adjustable from stock to stiff. The rear ARB is more straightforward but the front wasn't going to get done with the Nissan parts bin. This would give the ability to fettle stiffness without having to re-align everything again as with changing springs.
I am keen to add more camber to the front and rear wheels, also look at playing with the toe, to see if I can get the car to turn in better?In terms of simple things for your car, IIRC you can run more static front camber on your car. I've used -2.5deg on road/track with road tyres in the wet. This level worked on track but not as well on the road so I settled around -2deg as a compromise for dry/wet/road/track. For your fast lap you are looking at a smooth dry track with slicks, -2.5deg can be your starting point.
My current spring rates are 10kg/mm front and 7kg/mm rearspring rates are another thing that need to be mentioned, you need to run very very stiff springs if you are using slicks