You will want to keep the maximum speeds to be no more than what Bob did. This means that 30rpm on a 16" is like about 6rpm on the 35" mirror.
You also want to make sure that the table can support the mirror but you seem to be handling that with the casters (rubber ones) to support the sides of the table.
For the final pulley, you may want to make one in a mill with the appropiate cutters to make the groove. I`d make the pulley about 2` in diameter and allow for speed adjustments (go find the Mirror-O-Matic grinding machine on the web for some hints in that regard. I`d plan on a low speed of about 3rpm (for a 35" mirror) and a high of about 30rpm (for a 12" or so mirror) for the different pulley that you can put on the machine.
After you have that much done, you may want to make a convex disk so you can do grinding of mirrors of up to about 12" or so with the machine. A smooth sphere with shallow grooves about every 4" will be quite nice for doing the grinding.