Making your axle from scratch is a large undertaking, as you well know. Not impossible and you can do it. The thing is as a car builder not many people expect you to, nor do they expect you to cast your own motor. So don't be so concerned about being a bolt on parts guy, you can build all the mounting and what not while buying the axle.
Now, there is a reason why there aren't 8 and 9 inch dropped axles out there. The leverage created by that deep of a drop when you apply the brakes is much higher than with the lower drop, the axle wants to roll and it is putting a lot of stress on everything.
To make that deep of a drop on the short distance between the spring perch and the spindle is calling for some seriously tight bends, again, there is a reason why you can't buy one with that deep of a drop.
Just thoughts, don't want to kill your dream but you need to think why is it no one makes such a deep dropped axle? There are lots of new things out there to be discovered and created by a guy like you, just like there are a zillion songs yet someone will release one tomorrow that is new and fresh. There are lots of things not yet done on cars but that deep of an axle has been done and it hasn't been that successful which is why they don't make them, at least I have never seen one.