Have you thought about doing some porting work on your own? If you ask on here, info on what to do for starters to get about 50 to 75 percent of possible flow gains can be done by the average guy taking his time. You could start by working with the valves you have, or upgrading the intakes to 2.14 size. Just doing the intakes will keep the cost down, and I am betting on good gains, even leaving the exhausts stock. Some of the other posters here can maybe chime in on that last suggestion.
I have been thinking of doing some porting myself, I actually like that kind of work and have done a lot of 2-stroke porting, but the problem is lack of time... and iron heads will need long hours
The valves are 2.14/1.81s
Weight loss is another reason I've been looking at alu.
Buy the best you can afford at the time of purchase 
