Whatever you don't, *DON'T* sand-blast aluminium.
You will damage the frame.
Soft media blasting (plastic beads or similar) should be OK, or you can have it chemically-stripped (I had an alu frame chem-stripped for £30) and then polish it up afterwards.
If you have the time/effort/elbow grease, you could go the Nitromors route, although the newer Nitromors isn't as good, and takes a lot of effort. Some have reported good results with Gasket Remover also.