Disappointing dyno results
New balancer but timing mark not verified.
For sure, verify TDC with the positive-stop method, then check the total timing revved-up w/o the vacuum advance hose on & plugged. Shoot for 34°, then see what You have at idle, trust real..accurate timing marks...not dial-back lights. They can be off by enough that I won't use them any longer.
Next, Your cam is smaller than any 340HP cam, and the "closer to real NET" for the '72-'73 340 is 245hp. Even tho' they might have the smaller 1.88" intakes, You have a smaller cam, so that may make it a wash depending on the valve job quality.
Last, You keep saying "secondaries are opening", are You stating that the air-doors on top are opening? If so, are they opening fully? Next & last, but not least, Woodruff may have done a fine job of rebuilding the carb for You...but the float levels can get totally screwed by mis-handling during shipping. Just something else to consider.