It has been a while since I did much with the D jet system (I switched my 142 E to Megasquirt); however, the duration of the injector pulse width is not determined by the trigger contact dwell, it is determined by the analog circuits in the control box. The trigger contacts just initiate the injector pulse and provide an RPM signal to the control box. The Djet is a speed x density FI system so the RPM signal is probably more critical than the timing signal. My extremely fuzzy recollection was that the pulse initiates on trigger contacts going open (positive going signal); but, it could just as easily be set to trigger on contacts going closed (negative going signal). I would have to dig out the old schematics that I found for the Djet to be sure.

If the contact blocks are wearing down, it will be altering the point in the engine cycle that injection occurs; however, the D jet is a batch fire system so injector timing (as opposed to injector pulse duration) is not particularly critical. As long as you are getting distinct open and close indication on the two contacts as the distributor shaft is rotated the trigger contacts are not the source of your problems.

As I noted, I am getting fuzzy on Djet operation; however, any time you are having trouble around idle and transitions around idle, my recollection is that you should check both the set-up and operation of the throttle switch and the set up of the idle. I remember that a lot of people screw up the Djet by using the throttle stop screw to set idle speed rather than the air by-pass screw under the manifold. If you have not done it already, you should get the shop manual and check out the very specific procedure for adjusting idle speed, setting the throttle switch and checking the operation of the throttle switch. The operation of the throttle switch on the Djet is not like the throttle position sensor on modern FI systems.