It seems this truck has had 3 owners, so you might want to ask this person if they have done all of the work on this car.
Now if this Truck had an LS7 that puts out 505 Horsepower or so, might take a look at it. Now if it had a ZZ632 that puts out 1005 Horsepower or so, 45K is worth it. You need to make sure this guy is not a Flipper! Since he is the 3rd Owner, ask to speak with the second owner and verify what he paid for the car.
I have seen and heard of potential buyers getting so called Appraisers to go over the vehicle to give an honest opinion on what a car is worth. This truck has a 350 Badge on it, who put in the 383, you need to ask a lot of questions, and if you do not get any answers, move on.