cfm matters but its wet flow (MIXED FUEL/AIR ) not dry flow (just air at a constant velocity) on a flow bench,
that maters more and you want to keep port velocity fairly high.
of the heads listed that 300 cc looks impressive, but if I was building the engine Id personally still select the 315cc due to past experience, and thinking of the need for the larger port if I decide to install a wet nitrous plate.
as mentioned earlier, youll want too keep the piston speeds reasonable and valve train under control.
I don,t know at what point the low vacuum will become an issue ,
but neither cam listed will work power brakes,
https://www.summitracing.com/parts/...MI49uG9ZSr3AIVEdbACh0XWgzJEAQYAyABEgIN-fD_BwE
and the vacuum control on a trans or brakes set up to work on stock engine vacuum levels well .
there are options to increase vacuum.
http://garage.grumpysperformance.com/index.php?threads/trouble-shooting-brakes-3.380/#post-73632