Engine/Transmission (1998.5 - 2002) Transmission plug???

[P Madrid]

Guys, I need some help. At work we are replacing the transmission on one of our service trucks, 98 3500 24V. The problem is that the tail/OD housing has the speed sensor on the bottom but it also has the hole for the mechanical sensor that the 12V have. I spoke to a friend that use to work at a transmission shop, he said that a few transmissions from the factory came out this way due to the change over between the 12V and the 24V but a plug was install on the 24V set up. Does any one know where I can get this plug, my local dealers have no clue of what I'm talking about. I will try to post a picture. Thank You in advance.