Need Help W/ I.D.

Take a mirror on a stick or an extension and below the header and above the starter there will be #'s cast on the side of the block. Is the motor original to the truck? If so there will be an emissions tag that will give the liter capacity. You're looking for a 5.9 ltr. $3500 sounds a little high unless he can produce some reciepts on the build done by a reputable shop. Then was it stored correctly? I'd have to look it over close before i'd give $2000 for it. Does it run? I'd doubt it's a 340 but if so and you want to move it let me know.
Small Block