I was at a vintage BMW motorcycle show and observed many beautiful vintage engines, I asked them how they got the aluminum engine cases to look just right, I had several people tell me that sandblasting looks too dull and glass beading looks too glossy, they all agreed that blasting with walnut shells produced the correct look. Apparently disassembly is not needed, just mask off where you dont want blasted and have at it. I have not tried this yet, but I have used walnut shells to blast intake valves clean while the engine was assembled and it works very well.
John