340 sputter on initial acceleration

An HEI might really do you some good. It will provide much more spark energy and that starts a better kernal (initial spark) with a better burn.

Make sure that you points gap is set right. Being closed up a bit (which they will do with normal wear) can produce similar symptoms. Ditto for many worn/used ignition parts. Just replacing rhe PO's wrong ballast with a correct OEM ballast resistor on my '62 all original /6 points system made it fire better when cold.