The top trees don't have a casting number to look at. What I look at is where the fork stem hole meets the back edge. The early top tree that goes with the lower -52 tree has the hole meet the edges close to the top of the circle (see picture). The later top tree fork stem hole meets the back edges more in the center of the hole. I contend the change happened from the early to the later trees at VIN 2250 in 54, there is a good chance I am wrong with this assumption.