Sure, ideally a six-holer plate would be best. But let's look at what happens when a torque plate is bolted on a block:
The head bolts draw the cylinders outwards causing a squarish distortion at the deck surface. As you move down in the cylinder bore this distortion diminishes and the bore is rounder towards its bottom. Of course, cylinder pressures are highest at or near TDC (actually peak pressure is about 70 degrees after TDC, more-or-less, depending on the burn rate of the engine in question.) so near the top is where it is most important to have good round bores. Any deck plate to simulate this distortion is good - the square bore will be eliminated. Since the hone works on only one cylinder at a time a four cylinder plate should do an adequate job, particularly if the plate is overlapping in the adjacent nearest neighbor holes.
