When I did my LED conversion, I also put in a cluster that has a tach in my 97 blazer. I had to pop the tach needle off. And i also poped the fuel and volts needle off b/c they were faded, and the ones in my org cluster wern't so i swaped them.,
What i did was, fill my tank up all the way full. and park it over nite, than in the morning, i turned the ke to "ON" not running, SO all the neddels will register so i know where everthing is, than i ripped the cluster out, poped in the new one W/O the clear sheild, than turned the car "on", and placed the needles in the cluster. SO i know the tank was full, So i poped the fuel needle on to full, the engine wasn't running, So the tach neddle went on "0", and so on. It was preety easy. As far as accuracy goes the way i did it. Im dead on. So i hope this may help you
BTW, Could u toss up a pic. I wouln't mind seeing them in an actual car. Ive only seen them, not installed