[Dead Parrot]

It is possible that the previous bad carb was masking one or more other problems. Looking at the old spark plugs, it is likely the old carb was running way rich. If you also have a vacuum leak, the way rich carb can mask the leaning effect of the leak. If your new carb is perfect, and you didn't fix the vacuum leak, you now have a too lean condition, which often can cause backfire and misfires.

Now is a good time to check everything for leaks. Unless you know they are new, now is a good time to replace all of those vacuum hoses. It doesn't cost much to replace them and a bad one can cause a lot of headaches. Make sure your vacuum advance and Thermac pot are working. If you have power brakes, make sure that doesn't have a vacuum leak. Also make sure you didn't miss a vacuum connection on the carb. Qjets can have them in weird places.

Check things near the carb. It is possible you pulled, pushed or nudged something loose in the process of swapping carbs.

Any chance the suction line from the gas tank chose this point in time to fail? That can cause misfires on acceleration.