I wouldn't drill the holes either although it would look cool.
I was going to open up the speedo and at a minimum put the turn signal indicator in it.
On my speedmaster indicator lights could be seen on the headligh bucket if mounted low and to either side of the speedo which may look good and make them more user freindly.

If your ship doesn't come in - swim out to it ! Nothing but Triumph -'05 Speedmaster - Ride with the NorCal Presidents