The 450 GMC had a wider tread than the 2 tons. Putting air brakes on your Timken rear would take a lot of machining. The brake spiders for hydraulic or air are welded to the axle housing. Anything can be done. but what you are planning is going to be difficult to find parts and then a lot of labor when you find parts. Finding a donor truck is really the only feasible way to go. Your rear ratios will be too slow for a 3-53. And you will need a heavier suspension in front to handle the extra weight of the Detroit. Unless you have lotsa time and lotsa money, I wouldn't recommend even attempting what you want to do.