Brandant you’ve inspired me to make one. I need to dig into your WIP and put together a parts list. A surface grinder sure would take some grunt work and time out of flattening things.
Check out KenH's post
https://knifedogs.com/threads/surface-grinder.47166/ on page #3 post #45, Currenthill gives a pretty good parts list. I bought the linear slide table and linear rail that he lists there. I bought the magnets off of Amazon, the contact wheel from Sunray, and the aluminum from Online Metals.
I found that there were really five major parts that I had to build:
1. the magnetic chuck. Mine was made from 12" of 1"x2" aluminum with the magnets recessed in at regular intervals.
2. the tool arm. 1-1/2" square bar of aluminum to fit the grinder receiver.
3. an offset mounting bar to be able to mount the linear rail at an angle for ease of use. I used the left over piece of 1-1/2" bar from the tool arm. If you are building the attachment for a horizontal grinder, or you are willing to work the linear rail vertically, you can eliminate this part.
4. a mounting plate to attach the linear slide table to the bearings side of the linear rail. A 1/2" thick piece of aluminum about 6"x4"
5. the adjustable table. I milled mine from a 12" piece of 1"x2", but it could easily have been made by bolting two pieces of 1/2" stock together without milling. If you aren't worried about being able to adjust the grinder for tapering, this part can be eliminated and the magnetic chuck could be mounted directly on the linear rail.
Hopefully this gives you a good starting point to work from. Let me know if I can be of any help.