The stock front suspension will handle just fine. Virtually all truck over 1 ton are running the very same suspension design, and even Ford and Dodge still use a solid axle suspension on their 3/4 and 1 ton HD models. As far as better brakes or getting away from hard to find parts for the originals, there's
ways around that that do not require a frame swap or entire front suspension swap.
The engine should be plenty reliable, the GMC 6 is one of the best ever made. For more power, though, a later 270 or 302 GMC 6 would be a bolt in, no modifications needed. I would do the rearend swap to get better gears, and also look into a more modern single piece wheel with a more common size to run modern radial tires on. Set it up right, and you'll have a solid driver that will be every bit as reliable as a late model truck, possible even more so.
