I was wondering what this was and how do i get it off so i finish swappin tranny's

 

speedometer cable input, your new trans should already have one.

 

Well, its not a new transmission =[ its the original one. it got stuck in 1st so i just put a new one in. and a couple of weeks ago i brake the driveshaft and it hit the transmission and broke it. so me being 16 and poor i just pulled apart the original one and unjammed it. idk what happend to the piece. but is it possible to take it out... well it has to cuz we did it last time. just dont know how...

 

The speedo drive gear (which you have already unbolted) also has two seals (actually, a seal and an o-ring), which are creating some friction.
Just twist and pull and it should pop out.

 

You can also swap the tail section of the transmission, thats what I did.

 

Tap around it ..while Pulling Gently..the Aluminum around the Seal on it is usually Corroded and it Makes it hard to get off and out of the transmission.