The only photos I've seen of the jib boom crane mounting rings have been of dismounted turrets in Europe as war memorials. I readily admit to being in the dark on the finer details of Sherman turret production runs. It's true the early M4A1 76mm Shermans had most of the early T23 turrets without the rear ventilators because those were the first 76mm gun tanks produced. Now you know why I am using photos to validate all my Sherman models for the project.....

That will keep me relatively on the straight and narrow. Ya know, it's way past time for Joe DeMarco to write a book......
