833 question

I'm sure this has been asked before so I apologize in advance.i was under the impression that all 4spd. o.d.transmissions had an aluminum case.i just bought an 883 with a cast iron case so assumed it was a regular 4spd.today I see it's got the big retainer that only come on o.d.transmissions.so,what do you think I have?sorry,that's all the pics I have right now.thanks