I believe that what you need to sort out is how to do workholding on the part — once that is in place, then the problems of software and machining all fall into place.
What are the other dimensions of the part/stock?
Which machine do you have?
The official answer would be to use Gantry Shift:
and to bolt to the front of an SO5.1 Pro:
https://carbide3d.com/blog/shapeoko-51-pro/
If that’s not an option, let us know the specifics and we will look into this with you.