The Vac Secondary carb isn't helping. Recent episode of Engine Masters showed a significant increase in peak hp and tq with a double pumper on the dyno vs the same sized vac Secondary carbs. Logic being that as RPM increases the vacuum through the Secondary venturis pull additional fuel through the squirter nozzles of the dp carb. They have video confirming the phenomenon. Something like 15 hp if memory serves me. If you can source an 850 holley dp, give that a shot. More timing like others have suggested could help also. A larger double Pumper carb and timing sweeps are easy to do in comparison to a cam swap.Good luck.