I cant remember if this is going to be a trailer queen or you plan to drive it to the track...
If its to be trailered, ditching the PAS is a good thing. Saves weight, frees up a couple of horsepower from the engine as it doesnt have to drive the pump, and gives a lot more feel to the steering.
If its going to be used on the roads, even just for a few days a month, keep it. Non-assisted steering on the roads is a massive pain in the ar...ms... I'd advise against it.
The heater... trim it down, dont ditch it altogether. Rig up some kind of on/off switch and lose all the variable controls. Then ditch all the vents and ducting except the ones that go to the screen demisters. It rains sometimes... Without all those seat sponges, carpets and roof lining, the slightest bit of moisture on you or in the car will fog up the windows so you will need it.
Another option is some kind of aftermarket demister that runs off the battery, but they tend to be a bit rubbish.
Also, the heater matrix is an active part of the engines cooling system. Track use is very hard on engines. An hour or so on a tight twisty track without any time at high speed (with good airflow over the rad) tends to make things a bit warm under the bonnet. Using the heaters to get rid of a bit of that heat can be the difference between life and death (for the engine).
Are you planning on leaving the dash intact? They weigh a fair bit, and its weight to the front of the car too so helps to balance out all the weight lost at the back. A simple alloy sheet with whatever switches you need to keep in it is more than enough.
If you dont want to go that far, chopping it in half and just keeping the drivers side will shed a few kilo's.