HAve a look,at The 1 Ton. Build thread and you'll see where I put the CJ speedo..... 
I saw that, its not an ideal location for me, but may have to suffice, for all those who are suggesting electrickety, I would do but, and then I'd keep the TJ one, its the early short nose 300 with a square speedo cable that turns as fast as you drive, mechanical I believe they call it. The brantz takes a pulse off the mech cable and has a speedo on this. will this be sufficient for the MOT man?