Only 300 on the dyno means your engine isn't making the power it should or the dyno is wrong. Have you ran any timed 1/4 miles?
You combo should be making about 350 rwhp even with the mismatch of parts. So, maybe you should find out where the problem is before installing new parts. What is your total timing? Did you measure air/fuel ratio on the dyno? Checked cylinder pressure?
Yes, the cam and heads are too big for your combo. Get a smaller cam and head cc or add more cr, more gear, and more stall. A smaller cam would help but as you know already, those heads are killing low speed torque.
Typically heads that flow well don't need split durations or narrow lobe centers to aid in cylinder filling. However, narrower lobe centers will allow the intake valve to close earlier which will make more dynamic compression ratio and help low speed torque. Have you tried advancing the cam 4 more degrees?