Mortising the Slot for the Chipbreaker Nut
The original plane used a 3/4" wide by 1/2" deep slot to give enough clearance for the irons nut. I don't see any reason to change that here... so, using an awl, I mark the deepest location that the drill will reach with a 3/4" forstner bit, and start drilling a series of 1/2" deep holes.
When finished with the forstner bits, I chisel out the remainder of the slot using my bench chisels. Notice there's a bit of tearout at the top of the slot... that's because I was stupid and didn't continue the drilling above all the way to the top:
Luckily, I've still got some playroom on the height of the plane, and I can joint the top down a bit to remove the tearout. Once the slot is done, I assemble the iron and put it in the slot - sliding it up and down to make sure the nut has clearance for the entire length of the slot:
It surprised me! This iron hasn't been sharpened in probably 50 years (as you can see in the inset of the photo above) yet it was easily pulling shavings. The last person to sharpen and use the old plane was probably my great grandfather - so it's a testamant to his ability that it would still work so well, even after sitting in the weather for so long.