I when from a set of ported 360 heads to a stock set of 340X heads and picked up (went faster) 1 full sec. And my shift point when down from 7200 to 5800.
Yes these heads were my first attempt to port a set of heads.
All the ET was lost in the first 60 to 80 feet.
I say use the X heads and 404 cam. Eddys would work good to, and with the open chamber(340/360 chamber) The compression would be about the same..........don't you need one more point of compression for ALU ? :-k:-k:-k
P.S you can get new valve retainers that give you more retainer to guide/valve seal clearance.