Sounds like you have a 400B or possibly a 600b, a 530 or a 630. Those were the small case tractors with the Case-o-matic option during the late 1950s and 1960s.
To operate the Case-o-matic system, one engages the foot clutch which releases pressure to the torque converter, so that you can shift the transmission from neutral into a gear. Release the foot clutch and open the throttle, and the converter will operate very similar to an automobile with an automatic transmission. Once the tractor is moving under power, you can back off of the throttle momentarily and engage the system into direct drive by moving the lever on the right side of the dash down or aft. That lever engages the direct drive clutch within the converter, effectively bypassing the torque converter.
The lever on the right side of the torque tube is a high-low range selector which in combination with your main 4 speed transmission, gives you a total of 8 forward speeds, each with the com and direct drive settings.
It's a great setup. I bet you'll like it.