The bent washer is also on my ’29 and is probably what should be there. Looking at the step in diameter between the threads and spline, I would NOT recommend a split washer as it is likely to damage the end of the spline. If your car has the Gemmer steering box, the threads on the steering box output shaft are probably 7/8 diameter and 14 threads per inch, which is the standard UNF series. I would treat this shaft no more than a Grade 2 bolt, which has a recommended torque of 83 ft-lb. I agree with Ovid that the torque should be about 70 ft-lb as a conservative number. Using a little less torque will keep from stretching the threads. I treated mine as a bit less than the Grade 2, so will also end up about 70 when finished. With the bent tab restrainer, the nut will stay in place at this torque. Having a source of new restrainers available is a very good idea, as the tabs do not take many uses before breaking off, and most of our cars likely had this removed a time or two over the years. The only special feature of these retainers in the leg that goes down to hold around the Pitman arm and keep the whole assembly from rotating.
Once you have the nut off (1-1/2″ wrench), you are only half way done. The more difficult part is pulling the arm off the spline. It won’t fall off by itself. If you still have the fenders in place, a standard three leg pullers will not fit in this cramped area. I found a puller for the current F250 & F-350 (Lisle #41970) is short enough to fit. But you need to reverse a shorter (1 inch long) bolt so that it is on the inside of the puller, making it possible to fit under the fender / running board support and still get a wrench on it. Email me if you want some pictures of the modified puller.