Thanks to Bikenut for this excellent information.
Here is a list of replacement U-joints for the drive shaft on the 1st Gen Ventures. I have been running the B110 datson u-joint on my trike kit and it works great. Here is the list
1966 thru 1973 B110 Datson Car parts store
Trw 20128
Spicer 5-1500X
AEC 1064
Precision 392
Keith Yedica
Bikenut
Casco,Wisconsin
Before you go this route, please read the next post.