I noticed that the face of the spill plane was way out of square to the sides. Here is one way to remedy the problem. Use your marking gauge to set the width of the shallow side, then referencing the fence off the same flat surface, run the gauge along the thicker side and both ends. This shows you how much to remove with a handplane. Check your progress until it's square.
To make the wedge, lay a scrap piece, along with the plane iron, in the bed of the plane blank and mark it with a pencil. Leave extra length on the wedge until you're ready for final fitting. I roughed the shape out on a band saw and then planed it smooth.
To drill the escapement hole, I made a simple jig to hold the plane blank. The angle of the jig needs to match the angle of the cutting edge of the blade as it's resting in the bed*. I clamped the blank to a piece of scrapwood to support the forstner bit as it drills the hole.
Two pieces of walnut, one to sandwich the wedge and iron in the blank and the other for the escapement hole, are attached with screws. Once you attach the first piece, you can final-fit the wedge. Tap the wedge in, along with the plane iron, and wiggle it a bit to see if it is providing even pressure along the blade. If it wiggles, that means the wedge is not properly seated and is rubbing on a high spot. When you pull the wedge out, you will see shiny spots on the wood. That's where it's rubbing. Plane, scrape, sand, or file that off and keep re-checking the fit until the wedge secures the blade in place solidly.
Before final shaping of the plane, I just had to check to see if it works...it does! Now I have to make it look pretty by squaring up the ends, chamfering the edges, shaping the wedge, and giving it a shellac finish.
*This article was used extensively in making this plane. It provides construction details and photos that are a terrific reference.