I can add some information, based on research done back in 1980 by H.
L. Chadbourne of La Jolla, CA. Quoting from a letter of his to me:

"...I saw the name Ray Morehouse with call letters attached to one of
these ads [the QST ads] , so I looked him up in a recent callbook and
wrote him. Had a very nice letter back. He'd worked for Cardwell from
1924-1947. He had a little on the receiver, but referred me to Moe
Joffe in Los Angeles for more. Moe was directly in on the project.

....Allen D. Cardwell...toward the war's end...wanted to broaden the
product line. He talked with Grenby Mfg. Co. of Plainview, CT about
some sort of joint venture, with Cardwell doing R&D and Grenby as the
manufacturing arm. Grenby had started in 1940 and during WWII made
mainly parts for Pratt & Whitney. It was a sort of machine shop
operation. However at one point Lockheed gave them an electronic
assembly to make, and they liked the work, so decided on it for
postwar. Hence the Cardwell discussions. But the two firms could not
reach agreement and the talks ended by Grenby buying out Cardwell and
moving the firm to Plainville. Mack C. Jones, who had been an
engineer with Raytheon during WWII, was hired by Grenby as Ch.
Engineer, and he suggested the 54 receiver project. Moe Joffe was
under him.

"I had a fine phone conversation with Joffe and hope some time to
interview him in person. He said the 54 was a very advanced set, but
was not put into production because of its extremely high cost, $700 -
$800 a unit. The market did not seem to be there at the
time--possibly again, the huge supply of surplus put a damper on new
sales. Joffe eventually went on to Squires-Sanders and their
communications receiver projects."

I have Morehouse's letter here also; he said he didn't know what
became of the 54 prototype.

Alan