I suspect you'll have to raise the rear, and lower the front. BTW: Porsche set the rear spring plates so you can raise the rear, but not lower it. Hopefully for you, no one has messed with the suspension.

(But then again, why would the rear of your car be so low if no one messed with it?)

 

It sounds like you need a 911 expert to set up the car correctly, both front to rear and side to side. I agree with you that 24" is too low in the rear, and somewhere between 24.5 and 24.75 would be better. That will require a reset of the torsion bars, which works quite well in the right hands. The setup is done with protractors on the radius arm (spring plate), and then the car can be aligned and corner balanced. "Maxing out" the negative camber is not the right approach - your tire type, driving style, track use, etc., all have to be factored, and your clearance problem will probably be taken care of when the suspension/ride height is fixed. It'll cost you a few hundred bucks, but you will appreciate how well the car works when it's finished.
Pete

 

As pete said, the bolts are for fine tuning, you are really supposed to use a protractor and do it by re-splining the bars, then use the bolts to set corner weights.

I would lower it in the front, 25 inches is too high, euro height is I belive a little more than 23 inches, of course you will have the height set where you want it, Then corner weigh it again after all the monkey business, then an alignment to be proper (which is the only way unless its a Honda, then you get to cut coils!)