K and KB Frame? Same? Different?

Doing a little research on K and KB frames.
First the back story.
My 49' KB-2 has a little twist to it. Sits a little low on the LF, and also a little low on RR.
Suspecting a little twist in the rear frame rails, and spring sag on the LF, but have not got the measuring tools out yet.
Planning FatMan Fab MII for the front, and four link in the back side this winter, so figured I'd deal with it and sort it then.

While at Iron Invasion this past weekend I run into a friend of a friend who has a 46' K2 blasted and painted bare frame available.
The gears start turning. I might be able to get this frame and stick it on the chassis table to be sure its straight, to a roller state with the MII and four link, and then transfer my cab and bed over.

I could strip mine and do the same.

But how close is a 46' K2 frame to a 49' KB-2?
They are both 125" W.B. so that's a good start.
Anybody have some knowledge to share?

125" K and KB frames have same part number in the factory manual, there MAY be some slight improvements in a KB frame but essentially they are the same,

Thanks for the reply Jon!

Two recent experiences:
My beauty D-2 sagged and had a broken front spring because the original owner NEVER serviced it.
I replaced the spring and greased everything and voila! Sits even!
My K Series 351W Ford pickup sagged and had a BENT front axle. I WAS able to straighten the axle in a press but swapped in a good one, anyway.
Doesn't have to be the frame that causes the sag.

just like these old trucks, the older I get the more I tend to sag. not sure a new spring or axle is the remedy though...