727 valve body,

Many stock separator plates (but not all) had numbers punched out like that. Sorry but I have no idea what the 358 plate was originally used in but if you look the valve body over most of the time you'll find the last 2 yrs of mfg and casting #'s on the main body and channel plate. If you can make them out (some times their cast decent and sometimes their nearly unreadable) you can google what you find and maybe get an idea what it was from. The 3.2 lever is the next to the lowest ratio lever used so that says it's probably not from a real high performance application although as with any trans this old anything could have been changed over the yrs. It's not unusual to find a trans with parts and pieces from several yrs. if it's ever been rebuilt