I put 30-something thousand miles on a 59 Suburban with an original 283, and later a 307 V8 in it, and didn't have any steering system problems at all with the original straight axle and drum brakes. I kept up with traffic on the interstate at 70+ MPH for quite a while. As long as the kingpins, steering linkage, and wheel bearings are kept in good condition, and the wheels aligned, there's absolutely nothing wrong with that system.
The main advantage to swapping to the S-10 frame is the fact that parts are much more available than for the old straight axle system, people are more familiar with maintaining the IFS system, and power steering and disc brakes are original equipment on most of them. It's also nice to get your steering and suspension repair parts at the local parts store, rather than getting bent over a barrel without any lube by some hotrod shop when you need to replace a control arm, ball joint, tie rod, or something similar.
Jerry
