You always need to do a leakdown test to make sure you have no leaks. The intakes are notorious for leaking air. 93 octane will be fine in your motor.
The 300 main sounds borderline for a ported 4 mil. I would go up on main after no leaks are confirmed. Also check floats and adjust, could be running out of fuel up top. The lagging on bottom may be in the needle or air screw. Need to start out with needle in middle clip, air screw at 1.5 turns out from lightly seated all the way in. From here you will make adjustments. Need to know what pilot jets you have