This is from memory, the bigger hole is 32mm, and the other 3 x smaller - I used 5/8" from memory. Just check against another car first. I think last time I did it I dressed up the 3 x 16mm holes into 1 x slot as the holes actually overlap and look messy.

As another point of interest, see the dimple on the firewall photo directly above the RH edge (passenger's side edge) of the steering column hole? It is on the bit that slope backwards at about 45degrees. That is the dimple for a TH400 or TH350 speedo cable entry if anyone ever needs to know! I think it is also 32mm. The other hole to the driver's side of the column hole just gets a blank speedo cable grommet in it.