I still must be doing something incorrectly.

I've EXTRUDED the whole 2D drawing to 0.750" by typing:

- EXTRUDE > MODE > SOLID > SELECT DRAWING > SET THICKNESS

I've SUBTRACTED the large centre hole by typing:

- SUBTRACT > SELECT OUTER RING > ENTER > SELECT INNER RING > ENTER

I can then SUBTRACT the same way to create the through holes, but I can't seem to get the counter bores around the holes. Should I create the counter bore circles while the image is still in 2D, or should this be done once the drawing is in 3D and the through holes have been made?