Hi Brian,
Yes it's very confusing the dimensions as shown, over the years Stuart have redrawn models which eventually have some wrong dimensions and have been notified to them with no avail.
If you look at the cross section shown in the bottom middle of the drawing, it shows the O/A width as being19/32", go back to the dimension 7/32" on the steam passage.
Add 7/32+6/32" = 13/32"+ 6/32" = 19/32"which corresponds to the 2- 1/8" dia holes running horizontally as shown at 7/32" apart on the cross section mentioned , so the 7/32" dimension is correct.
However having machined several of these Oscillators I ignore the dimensions and set up thus.
Set the casting in the drill vice at 45Deg, mark off the holes to drill down into the 1/8" dia holes, remembering the one side is opposite to the other. ( see the diagram on the other side of the drawing)
Put your drill in the chuck and bring it so that you can see that it will go thro to break into the 1/8" horizontal hole ( show as 7/32" c.r.s ), lift the drill and bring it over the top of the casting and make sure that when drilling down to the 1/8" hole you cut into the top and bottom steam holes but be absolutely sure that you don't break into the cylinder pivot hole.
Spot drill the holes with your smallest centre drill after checking that you will catch the steam holes and miss the pivot hole.
You can of coarse check this out using the 7/32" centre if I have not explained my method clearly.
Here is pic of a casting with holes all plugged and Silver soldered in ready to be re machined, this was to help out a friend who just could not get to grips with the dimensions.
Best of luck George.