In 1996, GM produced a newer version of its electronically controlled 4L60E. This 4L60E transmission is 21-1/2" long, and has a removable bellhousing. It has a hex bolt pattern on the output side of the transmission, similar to a TH400.
The 51-0405 adapter was designed to make this style of 4L60E look just like a 700R. By incorporating a new clamp-on reluctor ring and sensor on this adapter, a 40 pulse per output shaft revolution signal is generated for the drivetrain control module. This adapter comes with a new clamp-on reluctor ring that should be installed on the new 700R output shaft that you have had installed in your transmission. This clamp-on reluctor ring clamps over the stock governor gear on the 700R output shaft. We have provided two reluctor sensor locations to choose from in the adapter. The hole not being used will need to be plugged with the plug provided.