Technical what type of transmission is in my 1937 gmc 1 1/2 ton?

Hello all . I am looking for a rebuild kit for my 1937 gmc 1 1/2 ton transmiision but for the life of me i canot figuer out what type of trans it is . It has no syncro , 4 speeds , one of wich is a granny gear . it also has a lock out lever for reverse .
When i looked at the Muncie trans it showed that they had brass sycro shims and mine does not.
it looks a bit like this one . but this one does not have the lock out for reverse . Any help will be nice .
Thanks

 

you have the older one. the one in the picture is the SM420, which was introduced in the late 40s. Yours is older.