As I have mentioned on here in an earlier post the company I used to work for designed/manufactured/cast/machined/assembledour Bullitt Mustang upper and lower intake manifolds, although I was not directly involved with this project(this being my area of expertise)...I would have to say the permanent mold for the casting and the corebox for the inside runner shapes of the intake are some where in the neighborhood of $60,000 - $80,000 a piece and of course they never only build one even for limited production runs such as the Bullitt. I would say atleast 2 -3 molds and 1 corebox as most companies can ill afford to shut down production lines if the tooling fails and need to be able to swap out tools for this reason, and for the fact that they needed 5,000 castings plus. So in conclusion can special aluminum valve covers be made, sure if the producer of the tooling-Patternshop, and foundry casting the product(valve covers) and the machining house that will machine castings, can all make it worth their while and sell enough to recoup there costs for the tooling it would be feasible. The best example I can give is if anyone remembers when the 5.0L Ford V8 was discontinued and the 4.6L came out, there was a few years gap before any speed parts came out due to the fact that the aftermarket companies need to not only design these parts around a new engine platform, they needed to see if the motor was going to really sell well to justify the cost for engineering/design/manufacturing these items.Sorry for the long rant...