To advance BASE timing, you need to jump E1+TE1 on the diag plug.
With the CEL flashing, and engine idling at 650rpms, you can shoot your timing gun at the crank pulley.
The timing gun should be clipped accordingly to the battery and the first or sixth spark plug cable.
To advance the base timing, you need to read the "check" marks that illuminate with the strobe of the timing gun. The block has numbers, 15 being the highest I believe,
Move the CPS till desired base timing appears.
HTH