diff looks fine. so, at the moment I'm on the hunt for a used 2nd gear pair. still need to finish inspecting all of the bearing surfaces but the only for sure item at the moment is the two 2nd gear cogs.
You are familiar with the North American sources?? New: Algar Ricambi USA Used: FerrParts GT Car parts TRutlands. As he posted above our Newman has a ton of 512s up in Canada. Several posts are urging you to closely examine the gear housing of the diff. Ferrari built it by welding two castings together around the perimeter of the bell. This weld is a known failure point at stock HP levels (as is the stock quill shaft). There's no way it will endure, at the levels you are pushing. An aftermarket piece is available.
came across a video I took while the car was on the dyno. love that music. https://www.youtube.com/watch?v=Uc31u_hXKBY