Have you considered the use of a step reamer? this might not work
because of the length of travel needed to go up inside the engine, but
a series of reamers might work. You won't have to drill or worry so
much about getting it 90 to the block, and when the hole is large
enough you could put in a pipe thread and screw in a plug drilled and
tapped with a smaller plug (do this on the bench, not under the car)
with about three wraps of teflon and you should be good for a long long
time.

The reason to tap the plug with the smaller drain is to not wear out
the threads in the block. It will take longer to drain the oil, but
that's no big deal, especially as it give you more time to sip whatever
wine you think goes best with an oil change (Austrailian Merlot for
petro, any light cab for synthetic provide a good place to start).

Jim