Realistic Expectations - 11 second Demon weekly driver

The 915 heads with that combo can get you 12.00 all day if ported a lil but by someone who can get an honest 260cfm. They start off at 220-228 cfm as cast iirr
Moderately to to fairly well ported should be close to 300cfm with those valve sizes.
Full boogie over 300 but the 906 will do more as an open chamber...@IQ52 would be the most experienced and more knowledgeable person to ask of the potential. I know I can get 280's out of a set with 2.08 int by .500-.550. As other said though.. it would be easier, more ootb to attain your goal with a set of aftermarket heads like 440 source or victors... but really you should see what you have and get test of what you think is the best looking port and the worst looking one and base you choice on that. For all you know... you already have 280's or the necessary flow.. and the rest may be drivetrain/suspension dialing.