That "aluminum" mag box and guard isn't really aluminum. It's actually an aluminum/zinc alloy (aluminum bronze) which is quite heavy. It is a similar material to that used for the Parker-Hale trigger housing.
It is pretty hard to make a mauser real light but seven and a half pounds all up is a pretty light rifle so you did pretty good. Looks pretty good too.
I've used a couple of those stocks and didn't mind them at all. GD
