What are the cam specs? Depending on the specs,you may not have enough compression to make up for the bleedoff,and that clifford is hurting your low end big time unless you are running a serious cam,and high compression.
Really your 65 should be as fast,or faster than your 70 based on mods to both,weight,transmission/gears.All im trying to say is that you may be leaving some power on the table with your slant car.
BTW I love that 65,its a badass car.