Just made my way through your thread, lots of progress in a couple of months! Nice work!
GM 4WD's have had an offset wheel track for as long as I can remember...claim is extra bite in un-touched ground. I've also heard they used off-the-shelf-axles instead of correct width to save $$. Choose whatever camp you want to believe.
Glad to see you went with green/yellow antifreeze instead of the Dexcool they came with, that stuff is straight garbage.
I went with the steel spacers for my K2500 Suburban...same company, but in the steel I think they call them Stahl. If you're not towing heavy loads, shouldn't make any difference, especially if they are torqued properly.
I may have missed it in the thread, but what is your intended purpose of the build? Just my own curiosity, and being nosy (haha), how does an import guy end up with a big block bruiser?