This is Bugatti T57 chassis number 57756 but not with its either original or current bodywork. I don't know who the coachbuilder was, in style a cross between a 101 and an XK120, but the client was the circus owner Jerome Medrano, probably done in the mid 50s. When sold in 2011 it had a more typical Atalante body. As you say, Bugatti provenance is not easy.