Ok I have a 75 a body 8 1/4 stock open carrier rear end gear ratio unknown probably 2 something.Looking at a used set of 3:55's.Need educated on what fits what.Seems like I've seen that depending on the carrier is what gear ratio will fit on it and that you can alter one to accept different gear ratios if so how?Are the splines different on the pinion gear from early to later years