He wouldn't have to know much to know more then me...I haven't worked on 100's but I have worked on mine 100 times haha!
I think he said he's put bearings in 4.I'm not doubting what he says, I have alot of respect for him and his help but, I know that I personally could never put new bearings on a scratched or grooved crank when I practically had it in my hand...except in a case like he's mentioned before where a customer wouldn't pay to have anything else done.
I would either leave it and not look or do it completely.
That's just me.... and I always tend to over-do everything.

 

Hey, here in the northeast if a set of bearings gets it running well enough to go another 50,000 miles until the frame rusts through then it's a perfect repair!

 

Well from that point of view I guess I would agree. The bearings will probably outlast the truck.

Everybody looks at things from different angles though I guess. My thoughts would be that when using new bearings on a grooved crank the oil that acts as a cushion between the crank and bearings will go into the grooves and there would be no cushion and the new bearings wouldn't get you another 50K.

and another way to look at it is if you built the engine to last, you could move it into a new truck when your old one breaks in half.

but really though, I guess the real question would be... if the bearings are shot and the frame's half shot...why not?

So I guess I've circled back around to ... he's right!

As far as the op's question, my dd has 150K and I have replaced the timing set, oil pump, head gaskets and all related gaskets and seals but haven't replaced the main or rod bearings and don't plan to until there is a reason to. It runs fine, it has decent oil pressure and on that one I'm sticking with the "if it ain't broke don't fix it" approach on most things.