Charlie Allnut

Hi, I'm in North West Kent in the UK. I drive/ ride 2,3 and 4 wheels. I'm currently fitting a th700r4 transmission to a 1950 IH L120 with a stock 220sd engine. I am about to connect the speedo cable to the drive on the transmission when I saw what looks like a small gearbox! I've removed it thinking it may be calibration compensator but it runs one to one. Can anybody educate me please, Regards Charlie