Spacers for Rega P3

I'm not sure what type of cartridge I have but it is not the original Rega. It seems taller.
Can anyone identify it (Nottingham ?)and figure out the height of spacer needed ?
http://picasaweb.google.com/100352153551466589742/UntitledAlbum#5500335753236383426

The photo of my cartridge again:
http://picasaweb.google.com/100352153551466589742/UntitledAlbum#5500335753236383426

I found it !
I have the "Nottingham Analogue Tracer 1".
The first one on this list:
http://www.vinylengine.com/cartridge_database.php?m=Nottingham+Analogue&t=any&mod=&sort=1&Search=Search&sty=&ovlo=&ovhi=&can=&dclo=&dchi=&stid=&masslo=&masshi=¬=&prlo=&prhi=
Now can anyone tell me the spacer I need ?

Thanks for the Thorough reply.
Will do as you suggested.

By the way, How tight should screws 1 & 2 in this picture be closed.
http://picasaweb.google.com/100352153551466589742/UntitledAlbum#5500866265439975474
I recently installed the Isokinetic cardas rewire kit (excellent upgrade) and had to mess with them. I ended up closing them in a way that allows me to adjust counter weight but use a bit of force in order to do it. I mean...is there a torque figure for that ?

Doug,

The result of your card test is 2mm.
The mid sounds much better now. Could 2 mm have such an effect ?
I'll order a 2mm spacer.