I had the same type of issue when I replaced the 24V spindle with the 611, and noticed that there was a .012" step when using my 3/4" wasteboard cutter. Turns out the bit was angled toward the front, although the issue was virtually invisible in all directions with a 1/8" bit. Here’s how I fixed it:
.097" of business card strips stuck in as shims at the top, along with longer screws to hold the vertical slide to the X-carriage. I’m sure there’s a more elegant solution, but for now it works just fine.