Re: whats it worth?
You have to consider a LOT of variables.
Is the title clean?
How many previous owners?
Where has the truck spent its life (southern and western trucks are desirable)
Any current mods to the drivetrain?
Upgraded brakes / propshafts / ECU?
Any rust?
Current mileage?
This particular truck looks well cared for. A built short block is @ $2000-2500 so you must add that to the sales price. Don't forget labor (calls for 23.4 hours to R/R and swap everything over to the short block). At $75/hr, that is another $1600.
Personally, I think $4000 is a generous offer going into this blind.
Absolute worst case, you can pull that (+ a lil) in parts, so you wouldn't be getting burnt either way. Might be the lighting (doubtful) or my eyes (possible) but the PS rear corner appears cracked. That piece alone is $350-400 in good shape used. All this must be considered in the final offer. All the best in your decision either way.