I remember hearing more than one complaint about the 1965 K heads having porosity issues and other problems a long time ago when they were being drag raced a lot shruggy work scope
Check the rocker arms for ratio, most of the OEM factory ductile iron ones suck horribly on the lift at the the valves, I've seen .130 lift differences at the retainers on factory stock stuff puke down scope

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)