I am new to this site and IMG_7952.jpgIMG_7953.jpg

I am hoping someone can help me. I have a 1980 K5 Blazer. I am pretty sure it's all stock. I broke the speedo cable and needed to make adjustments to the driven gear to accommodate for my 33 inch tires. Got that math all figured out. SO I order a new cable and the gear that conveniently came with the housing. In looking at this. My existing housing is threaded and has a metal 18 tooth gear. This housing is not threaded and the brown 39 tooth gear is plastic. Is any of this interchangeable? It appeared that the housing was the same for TH350 and TH400 Trans and that is what I ordered? But maybe I don't have that?? Need some help to figure this out. I can't seem to find the sleeve I have anywhere. Thanks in advance