Welcome to the site first off. Are you looking to make a 2wd crew cab or 4wd ? Do you want it long bed still or short bed ?
The easiest if you were to start with a crew like this one.
http://sacramento.craigslist.org/search/cto?s=200&query=gmc&srchType=T (need to scroll down on this page)
and swap out the running gear to make it 4wd if you wanted.
It is doable to do the way you described, just more labor intensive, and if you have to buy a crew anyway, it is better to start with a single rear axle. This is just 1 of the one's I have seen in the Sac craigslist. There are more around here that I have seen that have been on for awhile.
From your screen name I assumed you were in Oregon, which is not that much of a drive to start with the base you wanted first. The swapping of 4x4 over to a 2wd is not that hard if you have both trucks sitting there.
Just my opinion.
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