You may be right, and that makes sense. I seen the Blue C Bushings and new it was Duff right away, but the block looks homemade to me.
However I'm not an expert on 20 year old Duff parts, but have been buying from them off-and-on over many years. My suspension parts are all Duff & Wild Horses -because they make the best stuff.
Back in the day the Bronco owner probably didn't have many choices and this is the best he could come up with at the time. Fast forward, and now we have better quality parts and choices. So much easier to build/rebuild a Bronco now than 20 years ago!