C20 vs C10 frame question

[69GMC2004]

I'm doing some repair and crossmember replacement on my C20 frame. I'm converting the truck to a C10.

My C20 coil spring frame has a c-channel reinforcement section above the coil spring mounts in the rear, inside the frame rail. It's about 28" long. Does the C10 frame have the same reinforcement channel? Would you consider this a required reinforcement if you were going to box in some sections of the frame in that area?

Any help is appreciated, and pics of a C10 setup is a bonus!