You mention several things I want to ask about, and one that worries me a little.
I'll start with the worry.
I "shimmed" it using brass pipe connectors
In my experience brass isn't a structural metal, and is both soft and maybe a bit brittle. I'd worry that as you use the truck the brass is going to allow some movement, and as time goes by slop in the steering will develop, and perhaps those pipe connectors would crack and break.
I might be overly cautious, but steering and brakes are too important to take chances. Maybe I've got the wrong picture. If these pipe connectors are huge blocks of metal it may be fine, but what I picture is much thinner material.
Regarding the rear you plan to switch to, you call it a Ford type Dana 60. Is there a reason for choosing a Ford type? The Dana rears were used under GM and Dodge trucks too, and I'm just wondering why you would specify the Ford.
If you've mentioned your plan to go four wheel drive in other posts about this truck I've failed to notice. I'm curious how you intend to aproach that conversion. What transfer case you'll use, how you'll connect it to the transmission, and what front axle you'll use.
I have a set of 265/75-16 tires I've though about putting on my 1-ton. From your description the stock GMC wheels from a later truck may be a good choice in doing that. Can you email me some pictures, or tell me where they are posted? I'd love to see how yours looks with those wheels and tires.
