Help on 408 build

Nice heads, but not the main question IMHO. Chamber size is hardly changing so your static CR is not going down. That means you have to go with a 20 degree or so larger cam (for advertised duration) to get the dynamic CR down to the low to mid 8's.

That moves the engine operation away from 'smooth' idling street operation, but that being good or bad is a very subjective thing. Rougher idle, but with that DCR ought to still have good mid-range torque for the street. Quite workable IMHO, but just beware that idle/off-idle operation will be rough-er. Lots more power from mid range on up. That outcome might just be A-OK with you.

AL heads are an aid to stay away from detonation so that is good. With your present head gaskets, any anti-detonation aid from quench/squish is probably on the margin of being useful, based on common thinking. Tune will have to be done well and maintained well with this DCR level.

The plan is less invasive into the engine too; that certainly has its merits.