Well I've had it out briefly to test the speedo against a satnav (suspension is truly f*****) and the speedo is reading more accurately than the converted J-Spec one. All the wiring and converter is now back to stock, which I much prefer. Once the brakes go on I'll pretty much have a 50% UK spec!
The odo is also clocking up and displaying correctly and the dash is all back together, so I'm quite chuffed.
Will put my old Speedo (UK face) and converter up in the for sale section along with all the other gubbins I've accumulated if anyone wants any of it.