frame id? this is confusing????

[redbaron69]

i have read posts on were to locate the numbers on our truck frames (just behind the steering box and in between the cab mounts on driver side) i have a spare frame that i was going to paint new, bushings etc.. but my question is the last number is a 1... but it is a 6 lug drum front and rear??? maybe a 61??? what is/are the differances in a 61 frame to a 67-70? need a little help i dont want to put the time and money into something that i cant use. thanks