Have the carb and distributor been serviced at all or are they in original condition?
I had problems with my '70 318 getting it to idle smooth or at all when it was first woken up from a long slumber when I bought it.
I had the tank cleaned out along with the hard lines. All new rubber lines, a new fuel pump and filter.
When I could get it to idle, I kept chasing the timing all around. I rebuilt the distributor and of course cleaned and regreased the weights. The old grease on them was like tar. They were at the point where they might swing out or maybe not. If they did, they might stay out or maybe not. After that I was able to get the timing to at least hold steady but it still ran awful -missing, surging, bucking- and wouldn't idle unless I finger pumped the accelerator pump on the BBD.
I cleaned and rebuilt the carb and it was no better. I slapped on the '74 BBD from the engine my son was rebuilding and after plugging the extra vacuum ports I started it up and it idled smooth as silk. It's my daily driver now and is the best running car we own for crying out loud.
Could be a several issues and possibilities. Take what everyone is saying and begin eliminating them one by one. Good luck- That is one sweet looking ride.