Very common unfortunately. The crack/cracks will need to be welded (grind down around it, find the ends of the crack and drill them out so they don't spread farther, sometimes even after welding they can reopen or come back, but if you drill a hole at each end now it's "contained" to that one section. Then they sell braces to strengthen that part of the frame so it doesn't happen again, and it kind of acts like a patch panel as well.
Whole bunch of different vendors sell them, get whichever one you like best. They sell super cheap no-name kits and some that cost a little more, but none are terribly expensive. Basically just a chunk of metal that is the right shape to fit.
After a quick google search for "GM steering box crack repair" I found a bunch, and some how to videos too.
Rough Country C/K10 steering box frame brace
I'd probably go with this one just because I've had good luck with RC and I trust them, but you can get some for like 20 bucks if you really want to do it as cheap as possible.
I've also heard good things about the AutoFab gusset kit. More expensive, but is more than just a repair that beefs up the frame. After you weld the cracks their product is supposed to support it in a different way to take stress off of that part of the frame, wouldn't be a horrible idea to add one to a truck that wasn't even cracked yet just as a preventative measure. Should need this one for your 2wd truck:
AutoFab kit
As far as I know the other style of repair plate I mentioned before makes no difference because it's simply a plate for the frame, not a support bracket so the different style steering shouldn't make much of a difference there.
I might even consider doing both if this ever happens to my truck. Sure couldn't hurt