On Thu, 15 Mar 2012 13:43:35 -0500, Tim Wescott
wrote:

http://en.wikipedia.org/wiki/Schnuerle_porting


Set up a fixture to hold the cylinder liner at the angle you want the
port. Drill a hole to the largest diameter that fits your square port
and file to final shape.

If you are persnickety then leave the sleeve bore a few tenths
underside and lap of hone to final diameter after finish filing the
ports.

--
Cheers,

John B.