newish to me built 340 valiant feels sluggish. Timing?

Pull the vacuum advance line from distributor and plug it.

Use timing light and set idle timing to 15-16* BTDC. IF RPM increases, reset it to the 800-850 range and readjust the idle mix screws. That will get you 35-36 total with the switches where they are currently set.

I might change the vacuum advance slope to something a little more mellow, higher vacuum to get max advance.