Here is my experience with the speed screw, mine backed out far enough that I over-revved it and it cost me a cam, set of lifters, push-rods,valves,etc...
When I bought the truck it had a cracked timing cover, so when I had it out and torn down is when I learned about the KDP, it had already fell out! Its all better now....

What's a speed screw? The screw that limits full-throttle travel, or the full power screw that increases pump pressure?

In my experience, if you haven't tightened the lock-nut, the full power screw backs out and reduces pressure by its self; I haven't heard of it backing-in and increasing pressure.
Runaway is why you need to have a BegleStick ready to stick over your turbocharger inlet the first time you move your screw, and why you need to tighten that jam nut so that it doesn't move around on you. But also not to overtighten it because it likes to break where the O-ring is halfway down the threads...

I don't see how the high-idle screw could cause that kind of over-rev damage. I have mine fully back out, and the case of the pump itself limits throttle travel. Not to mention that no matter how much throttle travel you have, your engine speed should still be controlled by the pump governor.

What I call the speed screw is the high-idel screw, it was backed out al the way. When we put a tach. on it to set all the speeds to the CPL# it went over rated RPM untill we crancked that screw forward to limit the travel of the throtle linkage. Is the govenor on my pump screwed up? What other things cause over-rev?

First of all, the high idle screw isn't going to cause it to over-rev by itself. It's only going to let you get more RPM if you have the pedal down

But the stock governor set-up should limit RPM to a quasi-safe level (~3400 RPM), even with pedal down in neutral. In drive you shouldn't be able to get above 3000 RPM with the stock governor.

What RPM were you seeing when the engine self destructed?

I dont have a tach in my '91, we borrowed one from where my dad used to work, I had just finished putting in all my Banks stuff, on its first test drive, pulling a hill in 4th, pedal to the floor trying to make the pyro hit 1150 and POP, she died. The rest was expensive history. Sounds ike my gov has problems, the pump is totaly stock. That happened 5 years ago, have worked the heck out of the truck and have never had a probem since. I check the screw at every oil change and with a new screw and ocknut it hasnt moved since.
I've been thinking of adjusting the AFC starwheel and turning the fue screw in to the stop but I'm a little gun-shy with my pump mods on this one.

Sounds more to me like the cam walked out.

Did you mess with the cam retainer when you had the timing cover off to fix the KDP?

If you over-rev the engine, the first thing you typically hear is the valves tapping the pistons... Then you'd expect thrown retainers, broken springs... I've never heard of cams getting messed up due to high RPM's alone.

The cam retainer was was OK, used it on the new cam. I didnt hear any vavles floating because she was screaming. All the keepers were in place, no broken springs, just bent vavles, bent pushrods, some lifters had the recesed portion were the pushrod sets blew out, and a cam broke in three pieces. The valve train damage may have happened when I tried to start it again ater it died. I towed it back to the house and pulled all the rocker covers off, bumped it over and found only the first three sets of valves were moving. The KDP had fell out before all this because the timing cover had a chunk out of it already were the pin folowed one of the gears around and it went between the gear and the cover, breaking it. I didnt know about the KDP untill I found the pin in the bottom and started asking some Cummins guys some quiestions. I've came a long way on the B series since then.

sounds to me like you floated the valves, the valves stayed open, the piston hit them, slammed them shut and in the process bent them, shoved the rockers up and bent the push rods cause the cam was at full lift...........if the cam went flat the valves wouldnt open all the way up........

okay i'm still learnin about the ve pumps. this is an awesome post thank you. what i wanna know is can i [I]just[I] turn the smoke screw to create more smoke? or do i have to mess with everything else too?

You can just turn the smoke screw.