Frame and VIN help

[tx69gmc]

I am working on a cab off resto on my 69 GMC and have some questions for the experts. VIN is listed as CS10DSA29510. I suspect that the "D" in that should actually be a number but not sure. Cab plate says SA29510 and this is also stamped on the frame(under the cab on top of the frame rail). There is also 9B847711 stamped on the top of the frame by the steering box. What does the 9B847711 mean? Inside of glovebox also confirms the VIN and list the wheelbase as 115". It list model as CS1570D. Can anybody help me make sense of these numbers? Also in looking at the frame with cab off, I noticed several strips that are welded vertically on the frame in between the cab mounts. They are in the same spot on both sides. Is this some sort of frame repair. I know that truck was initially a manual V6 and has since been converted to V8 Auto. My intial assumption was that someone had turned a LWB into a SWB but VIN confirms that this is a SWB truck. I am confused.