87 frame longbed/shortbed

[t_graham11]

I recently bought an 87 longbed C10 for $150, is running. good glass good everything stored here on the west coast not driven on the salty roads so its sweet. Now, I've been researching and have came up with little information. there is two different frames built so 2 different size wheel base's 117.5 in (2985 mm) for short-bed and 131.5 in (3340 mm) for long-bed. I found these set of frame dimensions

http://www.chuckschevytruckpages.com/framespecs.html

Now when I frame differences are 14 inchs and the dimensions of the frame diagram is only showing a difference of 10? Its got me confused because I am trying to Shorten the Frame to a shortbed. It might sound silly but I bought the truck for cheap and the frame is good on it, and the front end is good. Does anybody have any suggestions or any information that could help me.... thanks for reading, Tony