Just FYI here, my '70 K10 has a factory inner brace on the inside of the frame. That's all it has ever had and it's still good. You may have something similar, as I can't find any where that says what years got what in the '67 to '72 stuff. Same thing with the front crossmember. ORD makes a bolt-in brace, but it only fits one style of crossmember. I custom built one for my son's '72 K10 since his had the different style and no inner brace.Yeah I haven't driven it much yet, basically have just been doing research and got some custom plates from the DMV, I can't wait to show them off when they get here, I'm surprised they weren't taken haha.
I've got to drive it a half mile or so to get it into my shop, but it's a straight line so I shouldn't be turning too much.
I honestly believe that these older frames were slightly thicker and less prone to cracking like the later trucks. But it's good to check and plan overkill in my opinion.