The kid at Oriellys gave a valiant effort to finding what I needed, but just couldn't find it. Talking with the Manager I said my next stop was at a driveshaft shop. If they didn't have what I needed I was going to have it built.
The store manager suggested
Northwest Drivetrain Service so I gave them a call. The man said the magic words. "I have what you need" and "we're open on Saturday ". Folks we have a winner!
What this conversion requires is a 1310 / 3R combo U joint. This uses external clips in the driveshaft and internal clips on the differential. This took some effort for a fairly common conversion but I feel like it's worth it. I went from a 12 bolt with 3.08 gears to a 10 bolt with 3.42 gears for less than $100.00