I doesn't appear that your question was answered.
On the 4 spd. Muncie transmission (at least on all of them I've seen and owned) you check the trans fluid via the vehicle speed sensor (VSS). The VSS reached from up top and is located on the driver's side rear of the transmission about even with where the cruise control actuator sits. It is pointing straight up and has a wiring connector attached to it. Loosen the keeper screw at its base and rotate the keeper tab to the side so it no longer engages the groove in the VSS. Now you can pull straight up on the VSS to remove it. You might have to twist it a bit to break the o-ring seal loose. Carefully lift it straight up as you remove it. The plastic speed sensor gear is on the bottom of the VSS shaft and is only held on by a small detent in the shaft. As you lift the VSS out ensure that the gear does not get caught on the trans case opening. The gear is almost the same size as the hole that the VSS is mounted in. If it gets caught on the gear case and you yank up on it the gear will fall off the VSS shaft and fall into the gearbox. There is little chance of fishing it out through the VSS mounting hole. Leaving it loose in the gear case is a bad idea also.
Once you get the VSS out (with the gear still attached to the shaft) you will see a line scribed around it very near the top of the part that sits inside the gearbox just below the o-ring. This is the high level mark for the lubricant. If you overfill the gearbox by too much it will blow out the breather vent near the shift mechanism shaft.