340 break in question

Two things I would do before start up.
[1] If the ign system uses electronic triggering [ ie, anything other than points ], I would set your initial timing at about 20*, not the factory 12*. It can be hard to accurately static time an electronic dist; the engine is more likely to fire having the dist advanced a few degrees, versus the timing being retarded.
[2] If you are using a mech fuel pump. Prime the carb. Leave till last, have everything ready to start. Pour fuel through the carb vent until fuel dribbles out of the primary boosters.