The wheel sits 20mm inside or outside the guard with a 6 inch wide wheel with a +25 offset???

on my car with 200b struts, lengthened control arms and 15x6 +20 offset wheels the wheel is still inside the guard.

But it sounds like you are trying to get the wheels in further if you are wanting to machine the wheel mounting down
But then wanting to lengthen the control arms to get more -camber, which would push the wheel out further

What size wheels and tyres are you running? 205/40 something it sounds like which on up to 15s or 16s shouldnt really be a problem

Using adjustable castor rods, it will pull the balljoint as far forward as you adjust the rod, or a little further coz its located further out on the control arms

too much camber, for the road more than a couple of degrees will probably see you going through tyres rather quick and not actually going round corners as well at normal street driving speeds due to the tyre contacting the road
Castor, dont think you will really be able to get too much, you will just have to cut your actual guard out so that the tyre doesnt catch it, and your steering will be heavier and have less lock the more caster you go