actually the '75 MY carb is a good one cuz Ma was now relying on the catcon to take care of alot of the emission requirements as opposed to the earlier discombobulated attempts to federally be emission legal with carb mods (73 MY is the worst) & the other timing systems you mentioned. Keep checking the carb since it being PT tells me the issue might be carb related & when resolved you might plumb the dist right to the carb (ported or manifold depending on what is available) for a power/mileage bennie & definitely bypass the EGR & rework the timing starting with initial.