Referring to the modified Mayfair Monte Carlo, supposedly two modified Mayfair Monte Carlo,s were sent to Henney and returned to Packard. It's nice to know that one of these two are still in existence and understand your maintaining confidentiality about this vehicle. Hopefully, someone can tell us what happened to the other Mayfair Monte Carlo.
Also, you mentioned the first late 1940's Monte Carlo designed by Richard Arbib had been destroyed but the components were in available to do somethind with. I understand that you are not at liberty to discuss any details.

Unfortunately, It does not have any pics of a prototype fastback.

I just received a new book "The Henney Motor Company a complete history" by Thomas McPherson. Pages 200 to 206 describe Henney's involvement with Packard in developing the Pan American and MonteCarlo with a few good pictures of the Pan American and one pic of the Monte Carlo. Overall the book is pricey but worth reading. A couple points of interest 1) Henney built the first Pan American for the auto show and Packard subseqwuently ordere 5 more, for a total of 6
pan Americans. I know that #1 was purchased and modified by McCauley and is on display in a museum in Detroit along with a gold colored one, and there is a green one owned by a private collector. This accounts for 3 out of 6 Pan Americans, does anyone know the where abouts of the other 3?
Also, the book supports that Henney built 2 Monte Carlo's for Packard, one is owned by a private collector, does anyone know what happened to the other Monte Carlo.
On looking at this this thread there are pics of the MonteCarlo, It would be nice if there were additional pics & information of the Monte Carlo & Pan American that could be shared or posted to this thread.