R150F vs R151F What's The Difference

Lately I've been researching on various options to swap my Tacoma to 4x4.

I currently have a 3.4 2003 PreRunner TRD package.

I have yet to make a choice wether I'll do AT or MT.

After much looking around I figured that the only option for MT 4x4 was the R150F transmission.

Yesterday I came up to a post selling a R151F MT that came off a 2002 Tacoma 3.4

So my question is what's the difference between both?

 

Pretty sure the R151f never came in the Tacoma.
Try this link, looks like it has some good information.
https://forum.ih8mud.com/threads/question-about-toyota-r151f-transmissions.1265506/