Transmission??

[Coltronist]

Hey! I have a 63 c10 and I made an interesting discovery that I don't have the original motor as I thought. I thought I had a 230 but it turns out it's a 250 inline 6 from a 67-72 c10 (I looked up the Casting number). Now with that being said, I have desperately been trying to identify the transmission I have connected to it.

It's a 3 on the tree manual column, There is NO pan under the transmission, and I found numbers just behind the bell housing on the drivers side that read 37219 as you can barely see in the picture.

Do you guys have any idea what transmission this is?