hi how can you tell what series of chevy 12 bolt rearend you have 1,2,3,4.is the 4 series a better rearend then the other series also can you take the axles out of a 56 chevy half ton 6 lug none posi rear and put them in a 1970 12 bolt monte carlo posi rear also does any won no if 70 monte rear end will be the same length as a 56 truck rear wanting to put a 70 monte 12 bolt posi rear in my 56 truck i know will have to weld new leaf seats on and different shock mounts or is there an easier way ,im not a pro by no means.thanks