I use marking gauges to make two marks, one for the set back and the other for the depth. For a long rebate like this one I will chisel a "V" groove. Then it is just a matter of riding the groove until you have a shoulder, as my clients would say "A sheet of cake".
First photo is of setting up:
The ECE rebate plane is a sweetheart, light, with a good iron, and it sets and holds well. Even better it doesn't cost much nor does it require work to set up like a vintage plane.
This is of the rebate about half done:
Last photo, testing the fit:
I still have not decided; does the tool box stay a tool box or is it the Grandpeanut's new toy box.