For telling if a part is cast, you can look at Rob's videos and see some of the "less important" surfaces of the front trunnion and bolt have itty bitty little craters on them. Like you're looking at the surface of the moon. The surfaces that are critical in shape/dimension have been machined. The part is cast and then machined in some areas afterwards.
Part that have been machined from a forging or a billet will not show the cratery rough surface. Those less important surfaces will just look machined. You may be able to see the patterns left in the surface by the cutting tool and is spins around and moves around the part.