Are you thinking the "072640" is a partial Chrysler part number? I spent some time researching it, but could not find a correlation with part numbers in the 1968 parts book. This isn't conclusive, because often, the "casting number" of a part does not directly match the "part number" in the dealer parts book. Further, because the yoke is part of an assembly, it's individual part number is likely unlisted in the book.
Your 741 (1967-1969 A-body) differential came with the smallest yoke of the (common) three types (741, 742 & 489) of cases, and measures at 1-3/8. But it may have been changed by a prior owner, so you may need to inspect further.
As you may already know, there are two basic sizes of the rear differential yoke, the smaller 7260 (2-1/8 width) and the larger 7290 (with 2-5/8 opening).
Sadly, these can be found in both the 10-spline and 29-spline varieties.
I seem to recall the NUT within the yoke is larger on the 29-spline yokes, compared to the 10-spline. The size, I'm not certain, may be 1-1/8 compared to 1-1/4?
What is wrong with the yoke you have, now? If you're replacing it, go ahead and remove the nut, as you can then see the number of splines behind the lock washer.