The ton frame is definitely different than a 1/2 or 3/4...unless it's a Crew. I too have a '79 dually that I'm going to convert. I was able to source all the components from a single cab K30 that I bought for parts. I cut the frame just behind the rear spring mount on the front so that I'd have whatever when the time comes.
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The 2wd rear spring hangers will have to be replaced in all four corners and replaced with 4wd; unless you want to run lift blocks. You can use all the 4wd spring hangers from a donor truck on the front but be advised that the front hanger is also the radiator support mount. I don't think there is any difference between the 4wd frames from the front cab mount forward so finding the front crossmember and mounts should be easier than finding the rear.
