1/4" thick spacer with 1/2" bore:
2" rub collar bearing with 3/4" bore:
Reducer for 3/4" ID to 1/2" bore required for above bearing:
2" OD straight cutter with 1/2" bore:
these should be all you need for the project.
Now, as to how to stack them ... bearing on top or bottom?
I don't think it makes much difference, more of a "will it work" on your arbor issue. How much does the arbor extend above the table at full height? Can you stack the components and still tighten the nut?
I would be concerned with a steel template on top for 2 reasons. If the template contacts the cutter...good bye cutter and watch out for shrapnel. The second reason if the template is on the top rather than resting on the table you will have to support the weight of the steel every time you make a pass... it will get very heavy. I would just make a MDF or plywood template, actually several to have a spare, to avoid these issues.
It's been about 10 months since your first post on this subject, and this thread was bumped, so, how have you been machining the boards since? Instead of using a shaper, have you tried a table router setup?I think we will replicate something similar to the video. definitely bearing on top for safety