You still have to drill the large 3/4"?? Hole first to place the tonearm base and feed the wire through. Center and measure that hole for your 222mm and you should be good. Then drill the other 3 screw holes.
BTW, I just drilled my 3 screws through the plinth and replaced the wood screws with 6-32 X 2" Stainless screws, washers, and nuts from the hardware store about $2.95. It sounds superb! This is on an RB700 nothing cheap about it.
D