Still don't see why you need source heads. What you have should work fine. Even with new heads if your distrib isn't curved right or is advancing way up you'll have the same issues. At 28* you should be able to run a 13.5:1 motor on pump gas...it'd run like poo poo but it'd run. Me thinks you have other issues, like timing and/or fuel delivery. Did you or did you not block off you cross over? running vac advance or not? using a stock distrib or one w/ light springs? I'd mess with that before I dropped $900+ for heads then another $2-300 to have them checked out.