The first question is do you have clear title to this? Some of the auction houses, like Sotheby's are leery of dealing with objects to which the ownership is unclear (they've been burned by, among other things, art looted by nazis) and the second, do you have a reliable provenance indicating it's genuine?
If the answer to both is "yes," check a few aviation museums to see who they use for appraisals (they do have to insure stuff, if nothing else) and who they would use to buy or sell stuff.