Biba - I don't have a copy of the original Alfa Romeo December 5, 1969 Service Bulletin that instructed dealers to shift the injection pump timing, but here's a summary of it from Alfa Owner:
TECHNICAL NOTE, Alfa Owner , January 1970
A new Alfa Romeo Service bulletin, issued December 5, 1969, advises a major shift in fuel injection timing for U.S. 1750 cars. The change applies to models 105.51, 105.62, and 105.71.
The change basically involves rotating the fuel injection pump pulley relative to the crankshaft so that the timing mark on the pump pulley lines up with its index at 70° BTDC rather than 80° ATDC as before. The change can be done by dealers by filing off the old "I" notch on the crank pulley measuring 1 9/l6 inches forward (clockwise as seen from the front) from the "M" mark, and inscribing a new notch to be used when setting the injection pump pulley relative to the toothed drive belt. It may be necessary to re-adjust the idle bleed jets after changing the injection pump timing. After the modification, the fuel delivery adjustment screw can be backed off to lean out the mixture, with the final setting to be determined by road testing. Some cars have already been set up this way at the factory; they can be identified by a spot of yellow paint on the protective cover over the pump drive belt. The following chart is a guide to telling if your car has this modification:
Alfa mod'l Some after Chassis No. All after Chassis No.
105. 51 1.530.748 1 530 769
105,62 1.481 196 1.481 373
105.71 1 555.770 1.555.799
The effect of the modification is to advance injection timing, lowering exhaust emissions and improving "driveability" and fuel consumption, according to the Bulletin. This modification, if applicable, will be accepted under warranty for cars in stock with dealers as well as those already on the road.