LD340 whats a fair price to pay for one these days?

Good price, have seen them go for a lot more. They are hard to find, and hard to find unmolested in good shape.

Check the thermostat threads and the carb mount threads for being stripped. Lots have been heli-coiled or not. Also check for corrosion at the water ports on the intake side.

Can also see if someone cut down the partition in the plenum.