Cracked frame - repair or trash it?

[Big Daddy Bear]

Been distracted by other priorties for quite awhile, but pulled the truck into the barn today so it could dry out before stripping the cab & bed off of the donor truck to start prepping the frame.

The frame has cracked at the top of the arch over the rear axel, it is broken clean through.

I want to build off a stock height, factory frame.

It took me awhile to find this doner truck, specifically for a stock frame, because the other one was butchered by a previous owner and unusable.

The butchered frame is a 3600, the damaged frame is a 3100 and the arched sections over the axels of the each frame are different. Could I cut a soild section out of both sides of the 3600 frame and replace it in the 3100?

Is it worth while to patch and reinforce the damaged area or toss it and go on the hunt for another frame??

Got to do a little resizing, then will have some pictures to add.

Thanks....