What build of ICS do I need for Nexus S baseband I9020XXKF1 Baseband version: I9020XXKF1

Current software build number is GRK39F on Android 2.3.6

I seem to have a pretty much unrecognised baseband version of the Nexus S. I brought mine carrier-free in the UK. 

There are a bunch of updates listed in this thread on XDA: http://forum.xda-developers.com/showthread.php?t=1063664

But there are 2 versions beginning with I9020, but they have extra letters on the end (no X like I do) : I9020A and I9020.

None of them match up perfectly, what update do I need/any dangers of using the wrong one?
My baseband is ever so slightly different from yours: it is I9020XXKI1 (I think; it's hard to read).  I upgraded by following the steps at http://www.androidcentral.com/how-manually-update-your-gsm-nexus-s-ice-cream-sandwich; I am pretty sure that you can't go wrong doing the same.  At worst, your phone will refuse to install the thing.