How do i change the speedometer on a 1989 camaro rs?

My camaro's top speed was 115 and that's what the speedometer reads. But i just put a performace chip and pretty soon switching my engine from 305 to 454. I just man-handled my dash trying to put a new speedometer in from a firebird--turns out they're not Compatible at all. I need to find a speedometer that will have a higher limit that is compatible with a 1989 camaro rs 5.7L 305. I dont know my axal rotation i dont know if that matters or if someone already knows it.