[tutone]

Every thing in your post answers all your Qs.
1.Its not an LS6 Z28 or Superbird
Its a higher optioned C10
2. Its a "real" 115" wheel base
Mine I cut down and its also 115
3. You think hes stiff on the price
Only option is talk him down
4. Good GM used tailgates are high
Fix that one and you spend days at it
5. Rust is universal
Make sure it is budgeted for
6. Is it a Big block? Cha-ching
7. Is it a 350? Not so much
Bottom line, the 115 on the SPID does account for something at resale time and that guy knows it. Can you live with the fact that it costs the same or more to restore a Cheyenne as it does a Custom Deluxe? Aftermarket chrome fits like crap in many instances, so NOS GM parts on certain things may be your best option.
I always take this attitude to the seller. "Is this gonna be a "forever" truck?"
Or Is this gonna be one to work on and keep a few years and sell later?
Either way, unless you give him enough to pay off his house, you probably will be ok in the long run. A factory swb in any trim will fetch some what better money. Also one more thing, look at the price tags on early gen camaros, mopar muscle cars, base or not, I feel these trucks are headed in the same direction, price wise. Good luck to you.