Frame differences??

[68shortfleet]

I have two questions here
First, I have numbers stamped into the sides of each frame rail right behind the front cab mount.
Drivers side 3913179-291
7-11-103
Passenger side 3913180-291
5-8-101

My vin is also stamped twice on the top of the left rail, once right behind the gearbox, and again right under the middle of the cab.
Can anybody tell me what the other numbers mean?? Not the vin.
Vin #ce148z105085

The second question relates to the frame metal thickness. My truck is a 68 c-10 swb. Some previous owner cut a little off the front frame at the bumper mounts, trying to install a roll pan? I got some front frame peices from a 71 c-20 frame to weld on. I discovered that the front body mount was located in a different spot in relation to the bumper bolt hole. I also found that the metal thickness was different. c-10 was .160 thick, c-20 was .190 thick.
Were all c-20 frame thicker like this? Does this mean that a c-20 frame that has been shortened could actually be a stronger, better handling frame than a factory c-10 frame?

Thanks
Jason