Vision block riser was B Mod. (also the L shaped bracket forward of the cupola … to keep the .50 from shooting the searchlight) Ma Deuce on the cupola top ws a field mod. I’ve seen photos of ones with the one in the cupola and one on top. Just the one on top, even one with twin .50s on the top. Another pic I saw had a .30 cal (forget the designation but was an M1919 rechambered for 7.62 NATO) rigged up for the loader’s hatch.
B31 with .30 cal on cupola. 
.50 for loader.
