Keith,
It sounds like you removed the top rockshaft for the rear lift, if you removed a long pin. The drawbar is the triangle at the bottom with the hole in it to pull a trailer with. It's held on with the bottom 3 bolts of the back cover, and may also have the bottom U shaped bracket for the rear 3 point hitch (that is what IH calls the top rock shaft and lower u bracket).
As to removing the cover, yes it is important. Hy-Tran is hydroscopic (will absorb water) and will create little globs (similar to corn starch if it doesn't get mixed well) These globs will settle to the bottom, and need to be removed. I believe this is why IH didn't put in a drain plug. Trust me, you want the water out of the fluid. I used a "hy-tran compliant fluid" that did not en-train and remove the water. The pump whined more than it should, and when I changed the fluid (for Hy-Tran) the fluid I took out was still the correct viscosity, but was the color of peanut butter, because of all the emulsified water. Once I had the correct fluid, it doesn't whine as much. The main thing to make sure you don't have a leak, is make the surface surgically clean, and make sure the bolts go back in the hole they came out of. Because depending on what is bolted to the outside, like just the drawbar, or the drrawbar and U bracket, a tiller hitch, etc will change the length of the bolt. The wrong bolt can pop the bolt hole in the transmission case and cause a leak......