Caustic soda will eat away the bare aluminium, leaving pits.
There's nothing that will eat the anodising and not the ally - anodising is a surface protection put on because it's more haard wearing than the bare metal.
Chromic acid should do it without removing the base metal but it is a very nasty substance and not so easy to get.
Anything abrasive will remove the bare metal quicker than the anodised metal, so again you'll see pitting.
tough job with no easy path. I'd suggest speaking to restoration specialists - classic car places, etc. Or maybe find an anodiser locally that might be able to help out?
Si