8 1/4 or 8 3/4 rear end in my Duster 340?

I was at a big cruise meet at Gillette stadium the other night because I am selling my '73 Duster 340. It recieved a lot of attention with people crawling all over and under the car and one thing that came up was the rear end. From the old days I remember the 8 3/4 rearend being the smooth on the back front mount pumpkin type. I think they were called hotchkiss while the 8 1/4 was the rear cover plate style called salisbury. Well my matching numbers 340 appears to have a 8 1/4 in it but the 1973 sales brochure clearly states that the 340 package came with an 8 3/4 axle. Did they ever make a rear load 8 3/4 set up. Did they run out of 8 3/4 rear ends the day my car was being built and just threw in the 8 1/4? Any ideas out there?