No, they appear to have been fully functioning turret mounts, even some advantages in elevation due to the greatly reduced bulk of the piece.
Objectively we can't really dismiss these engineers so easily just because they were on the ranges mate, many more less peculiar/conventional designs enjoyed far less auspicious first testings & trials.
This appears to have been serious work that convinced serious men that in view of the materials shortage it was well worth taking forward. If it was many other authors I might raise an eyebrow too, but as it's Spielberger the account is somewhat more intriguing.

Cheers,
Adam.

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