Slant Six has No power. will not accelerate

My 69 Dart 225 idled like that - rough and wanted to die in D or R, though I had ample power off idle. I just hated worrying about it dying at a stop light (drove w/ 2 feet). When it still acted the same even after a totally new long block, I tried my ~4th Holley 1920 carb and it ran amazingly smooth. The problem is that the metering block is sealed in those, so can't be truly rebuilt. One guy here reported luck in blowing it out from a hole in the base of the carb (off engine). When it acts up, close the choke plate a bit and see if it smooths out. If so, it is running lean at idle.

Re distributor, rather than fool with yours, I suggest start looking for an electronic one (71+) and using an HEI module with it, as many her have. BTW, mine still idled rough with a Holley XR700 electronic ignition on it, so don't expect better ignition to cure all. Your low power problem could be from poor spark timing. Give it as much advance as it likes, until you start getting pinging going up hills. Use a timing light (cheap at garage sales) to insure the timing increases ~30 deg as you rev the engine, or spring for a new light w/ digital delay (~$30 Amazon) to measure exactly. The suggestions that "50 mph max is typical" is total bunk. These engines were used in trucks and full-size vans. One guy added a turbo and runs 10 sec qtr miles. When the slant first came out, one guy even ran a drag rail with one.