For the last few years, we've done exact sizing for the bearing Outer Diameter (OD) and just deburred the edges of the holes. For a 1.125" OD bearing, we model exactly 1.125" in CAD and the cut parts come out as a very light press fit for the bearings. We press them in using a socket and a vise. The OD of the bearings we've accumulated over the years vary by about half a thousandth; the large ones need a vice to press in and the smaller ones can be forced in by hand..
0.003" is added between each set of meshing gears to make up for gear tolerances, and we haven't had any gearbox related issues so far. All of our gearbox plates have been 0.125" 6061 aluminum.
For those in Phoenix, we've been getting help from MarZee and have had fantastic results.
http://www.marzee.com/