[LostMy65]

I only went with the 62 frame because back in 84 I didn't know right off the differences.
My friend Todd's dad offered me the 62 gmc for a donor to rebuild my 65 after I totalled it.
If I knew what I know now, I would have looked for a shortbed 66.
But getting it back, I'll be keeping it on the 62 frame because of memories and nostalgic reasons.
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With the upgrades you want to do to your truck, I would think the newer frames would be the better choice.
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Now, I heard the reason they changed the cab in 64 was because more twisting of the 63+ frame was putting much strain on the wrap-around window style cab. So they redesigned the cab's front pillars to create more of an 'A-Frame' structure to the cab.
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And yet, I haven't heard any complaints from those who have a 63 as this being an issue.
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As to your other question; the rear cab mounts are the same. It's the front cab mounts that are different, but still easily works.
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Shortening a 60-62 frame would probably be way too much work.
Me, I wouldn't attempt it.
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From reading these forums, Shortening a 63-66 frame doesn't seem to be that difficult at all.
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