Chris,
Thanks! I've always wanted to make a plow for myself, and this event gives the kick in the tail to get it done. The arm mortises are 3/4" square and were first drilled out with a 1/2" center bit, working from both sides. This gave a place for the chips to go, making the final cleanup much, much easier. The same process was used for the depth stop mortise and the bed, although I used a long nose auger to drill out for the bed. I'm not done paring the bed perfectly flat yet, but I won't do that until I'm ready to fit the wedge, since the iron will only really contact the bed at the top and then on the skate. Two points of contact and tension from the wedge will make a very nice fit. This is the case on several of the old plows that I have, so I'm copying it.
I hope it turns out!
Your endgrain is like your bellybutton. Yes, I know you have it. No, I don't want to see it.