My 340 in my 66 developed issues :-(
Not to influence you here (or suggest GM parts - I know folks are a bit sensitive about it), but since your Valiant is from the points era, you might want to try running a GM HEI ECU hidden under your distributor with a Designed2Drive adapter. The HEI unit lets you run a low-resistance coil and open your plug gaps a bit wider for a hotter spark.
Best bit is that the combo hides under the distributor so well that it'll look like you're still running points:
I left the ballast resistor on the firewall in my build, but soldered in a solid wire between the tangs. (EDIT: Don't do this with a stock system).
-Kurt
Not to influence you here (or suggest GM parts - I know folks are a bit sensitive about it), but since your Valiant is from the points era, you might want to try running a GM HEI ECU hidden under your distributor with a Designed2Drive adapter. The HEI unit lets you run a low-resistance coil and open your plug gaps a bit wider for a hotter spark.
Best bit is that the combo hides under the distributor so well that it'll look like you're still running points:
I left the ballast resistor on the firewall in my build, but soldered in a solid wire between the tangs. (EDIT: Don't do this with a stock system).
-Kurt