You are correct tractor is 1946. Engine s/n makes it late 1948 or more likely early 1949 from a WD.
Most likely if you look really close you will find WD prefix and GA suffix where s/n is stamped on left side of block behind carb. It could also be K suffix but GA most common. GA would have originally been a 5.5:1 Compression.
About mid 1951, suffix changed to PA indicating 5.7:1 CR. But by now there is no telling whats inside - could even have WD45 parts