Proctologically Violated©® wrote:
...
*Finally* accomplished said task, and, big big bummer, the reception of the
car radio in my shop/garage is even worse than my home radios/stereos!
Yet, this *same radio*, when I used to park the car this very same garage,
had great reception.
...

Been decades since I have taken a car radio and placed it in a cabinet
with its' own speaker(s), power supply, etc. and created a "Miracle Kludge."

However, if I remember correctly, I found the same as you, poor
reception--until I tuned the antenna adjusting capacitor (was a hole on
the back of the radio turned with a screw driver.) It then turned out
to be the most sensitive am set I ever owned (well, for one without a
long-wire antenna attached.)

The antenna is part of an "antenna system" of which, the car body is a
part with much influence ... ditch the car body and you have to readjust
the antenna.

Regards,
JS