I had my stock head reworked to increase the cr to 9.5:1, new valves, springs, guides and had it ported and polished and the head flowed with the intake. Along with the other improvements I already had (trips, etc.) I spent way, way under a grand, including shipping, to achieve what I feel is close to the PI unit in performance. I added the GP2 cam and custom-length chrome-moly push rods and tuning it is a charm.
Al head would add major bucks to this and not achieve much more in the way of performance, except to lose about 40 lbs.
(and that is not British lbs.)
Bill