I don't have any better pictures than what I've added below, but this '73 had a custom sliding window in the factory half cab along with a vertical bulkhead. The bulkhead touched the front edge of the rear wheel wells. By making it vertical, there was around a foot of cargo room behind the seats where the guy I bought the Bronco from had speaker boxes. Without the speaker boxes, you might have been able to squeeze a bag of golf clubs back there. It wasn't a ton of room, but clearly more than the stock angled bulkhead.
I sold this Bronco probably a decade ago now, so can't get any further pictures.