Hey Drop where did you order your UV joints??
I am going to add some info this old thread. I am prsently involved in changing the U-joint on my Car.
On another forum it has that the direct fit U-joint is a Lobro ((Also may be written LÃ–BRO or LEOBRO) U728/4. That brand name is part of the GKN company.
I located the site below and if you search with the U726/4 or you search with my 83 300D I got the info below.
Above All Motorwerks - Select Year-Select Make-Select Model - Above All Motorwerks
Driveshaft U-Joint (2 Needed Per Car)- 22 2537 031
Ch. # 123- 123 - More than 10 IN STOCK - $ 24.45
[Note, I only have one U-joint on my car but apparently some 123s had 3 piece Drive Shafts that have 2 U-joints.]
However, I used the 22 2537 031 part number and did a part number search at Autohausaz and it appeared to cross reference to 9004100031 for about $18.
Since Autohausaz has free shipping if you order more than $50 I ordered some other stuff and the 9004100031 U-joint (I decided to take a chance that it was the right one).
I am still waiting for the U-joint to arrive so I am not sure if it is the correct one or not.
I also found another number from one of the GKN companies that makes U-joints Uni Cardan reference #18725 Cross references to the Lobro U727/4
If you live in Australia Hardy Spicer #K5-A657 may be the correct number