NG, that's correct, those shims are for setting preload, same for any other machine spindle. Considering the bearings you removed are either magneto or angular contacts, thats all I would be searching for to replace the originals with.
I wouldn't want you to destroy your grinder because someone recommends changing them to another format. I like the fact you're not scared to take on a job like this because in reality it is simple, its the bearing adjustments that cause the most grief.
cheers