Cool. Tune-up parts and technique suggestions in
this post. See to the
valve adjustment, too.
Power or none, the 9-inch drum brakes were adequate for the lightweight '64 Valiant in 1964 traffic. They were questionably adequate on the larger, heavier Dart, and their inadequacy grew less and less arguable as the cars got heavier and the traffic got denser. There's a variety of good options for upgrading. See
this thread (login required and worthwhile).
Save yourself an enormous amount of hassle;
www.cunifer.com instead of steel. Also do the
Fuel line mod.
See
here and
here and
here for advice on where to (and where not to) buy parts.
Do the
HEI upgrade .
Yes, but you're better off getting a better-than-stock setup built by a good local exhaust shop. Good recipe is
here; it works just as well (with a 2-1/4" headpipe) for an upgraded stock single exhaust.