So just to recap, problem was;
1) Tacho didn't work on the auto dials, but speedo ok?
Dials changed for manual dials.
2) Tacho still doesn't work on the new manual dials but the speedo now over-reads? Everything else on the dials works fine?
No other work carried out between 1) and 2)?
(I'm not sure where all the ECU swapping / chip swapping shenanigans fits into this sequence?)
Phil's covered the tacho fault and I agree, it sounds like a km/mph convertor problem for the speedo. (Phil, I PM'd you before reading the rest of the thread btw, which then answered the PM

)
If the speedo was fine before but now over-reads and nothing else on the car was changed in between the old dials working ok and the new ones not, could it be that the convertor was fitted to the original dials and so it was removed with them, meaning the new speedo is now reading kmh on the mph markings? (although 30 mph isn't 60 kph, it's 48

)
Maybe?
Can you post up some pics of the front/back of the old and new dials?
And just clarify the exact steps of the symptom/work carried out on the car.
Might also be useful if you can post up pics of the stickers on the cases of the 2 ECU's (the rectangular sticker with the part/serial number on)?