1971 rearend 741 case questions

My son bought a 1971 dodge dart for the 8 3/4 it has. We got it pulled out and see it's a 741 case with 2.76 years in it. He is putting it in his 1971 Plymouth valiant, which is a 318 car, 904 trans and currently a 7.25. I know we need to use the driveline from the dart as the difference in wheelbase. The dart is a 318/904 as well. Car is rusted beyond any reasonable repair. My question is this, my son was wanting to put 3.23 years in the 741 case? But I'm finding out that no one in the aftermath world makes a set of 3.23 gears for a 741 case. His car currently has 2.76 gears in the 7.25, so it's not like he cant live with it. I spoke with Strange, they said nope. Nothing for the 741, Dr. Diff said he has 3.55 and 3.91. But have to upgrade our pinion to a 29 spline from the stock 10 spline. Total cost for gears, bearings, spline around $340.00 not horrible at all. He did say that he is making 3.23 for the Dana 60 and is heavily debating adding that gearset ro his 741 line up. What are my options? Beyond buying a 742 or 489 case. Did Chrysler make a 3.23 in a 741 ever? Do they come up for sale?