Good find!
I would venture to say that a 1965 348 truck engine in basic running condition would be worth $500 - $1000 depending on what your plans are.
Some of the parts are not components one might want on a passenger car, such as the water pump, the distributor and maybe the intake/carb setup. It costs $$$$ to replace those, so you might factor that in.
These 348s do use the 409 truck oil pan, so don't be fooled into thinking it's a 409 truck engine, which might be worth a bit more.
The block will likely be a "655" casting, the heads will probably be the 333s. Keep the oil pan and the valve covers.
I purchased a "stuck" engine similar to this a few years back (3-4-5) and the guy wanted $500, I offered him $100 and he balked for a while, but let me have it for a hundred bucks.
Hope that helps some, others will have an opinion to add
.
Good luck!
TomK