They smoke like that because they turn up the fuel volume whether it be via a mechanical pump or a computer chip, problem is without a larger turbo they can't get a proper air fuel mix and all that black smoke is just wasted unburned fuel...
Have a complete 304 with all accessories less the intake( its there but i think its cracked)I'm willing to trade for a T-18 trans. The engine ran when I pulled it but it needs rebuilding.. PM me if interested, I'm in central Cali
Then you have a vacuum advance, remove the line from the carb and with the dist cap off put suction on the line and see if the advance is working and holding
Recently got a 76 CJ5 with a 3 inch susp lift, whoever lifted it used 1 inch spacers between the skid plate and the frame to lower the T-case, does anyone know if that's even necessary with that amount of lift, or maybe not enough ?
Have you checked to see if you distributor is advancing, that could make it stumble, even if your diaphragm is good you could have a broken spring or even a worn distributor
If you start drilling slowly and carefully keeping the bit in the center if the bolt then stepping ip to a bigger bit you might get lucky and be able to peel out what's left of the bolt with out damaging the threads in the hole