Quench head for /6 ???
There are VERY FEW aluminum slant heads floating around, all prototypes from the 70's. Even the "aluminum" slant had an iron head, on an aluminum block. No such thing as an "aftermarket" aluminum head, lots have been talked about but none ever made it past the "talking" stage. It is said over on slantsix.org that the peanut plug head is a little better then the drool tube head. Factory heads are your only option without spending HUGE money.
TopHat