I have a 67 C20 Chevy 2wd that I would like to add 4wd. It has been restored for driving so I would like to add on to the existing frame rather then take the fenders and cab off. Were the 2wd and 4x4 frames the same from the factory? I have modified the rear end and plan to also put leaf springs in the rear rather then the coil that are in it now. I would imagine a front axle from 67 to 72 would bolt in with the springs and would require a new power steering pump and some other things. Would a front axle from 73 to 88 fit with the same modifications? The axle should be similar but would the springs be the same? Also what work would need to be done to the crossmember (350 - 350th auto) to accept the transfer case. The rear end also has 3:73 gears right now. Any advice would be appreciated.

The newer axles will fit as the spring perches for the front axles are the same, and the only difference for the rear is for P-series, and 1-ton, but they can be modified for use cheaply.

I have no clue about your frame and the interchangeability with the 4X4, but the later 73-87 use the same frames, and I am doing the exact same swap on my 88 Suburban when the weather breaks and overtime at work to fund my projects slows down.

It depends on how much higher you will end up going, you might be much easier and cheaper off leaving the coil sprung rear in there and just using taller coils.

You will also have to change the steering box to a 4 wheel drive unit if those differ for your series truck, I can get away with swapping the arm on mine.
I can maesure one of the later series frames for you and you can go from there to see if you can make the changes to your truck if you want, I just can't guarantee it will be really soon though.

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