318 Running Rough / Backfiring

For the leaner plugs in the back, I suspect you either have:
- a leak in the intake system near the back of the carb
- the secondary throttle stop screw is too far open in the

Either of the above will add air into intake, and due to the position of where the excess air is coming in, the back cylinders will lean out more. The overall mixture richness has been increased to make the rear cylinders idle OK, but that makes the front cylinders over-rich. Seen this happen before with a too-far-open secondary stop screw. Some cylinder-to-cylinder mixture variation is common but your 1-to-7 mixture variation is huge.

It also looks like the carb may be rich at other phases of operation, so IMHO, some carb work is in order. With cooler weather now, the electric choke is closing up more and staying on longer after a cold start, and that may be the base issue with all the carbon fouling on your plugs; simply adjusting the choke a bit leaner may help reduce the richness. Silly question: Is this your first carbed engine? It's just that the start up process for carbs versus FI requires a lot more 'user involvement' and sometimes tweaking on the choke system as the seasons change.

Things like idle vacuum and PCV and power valves can interact to mess up mixtures. What PCV valve is in there? (A Mopar OEM PCV valve won't match up well with this cam.) And what has been the idle vacuum level? With your cam and such, it ought to easily tune up to around 13-14" idle vacuum at 800-900 RPM. If you have less, then it needs work on PCV valve selection and setting the secondary stop screw.