Put some 66 or 67 273/318 heads on it... They are still closed chamber and will have the 'new' bolt diameter and angle where you can use any "LA" engine intake and not the special 64 - 65 intakes which are fewer and farther between....
Also be sure to replace the timing chain with a double roller... The stock 273/318 timing chains are junk and stretch too easy and may jump a tooth...