Ahhh... there are multiple settings in Settings.php that need to match what you've put in your (working) GR3-radar-inc.php script.
GR3-radar-inc.php has
$GR3radar = 'kccx'; // set to lower-case full name of NEXRAD radar site (ICAO)
$GR3DIR = '/images/'; // set to directory for GRLevel3 images (or '/' for root directory
$GR3type = 'br1'; // default radar image type 'cr','br','cr248','br1' etc.
$GR3img = 'jpg'; // GR3 image type 'jpg' or 'png'
$GR3cnt = 10; // number of images in series 10=(_0 ... _9 in name of file)
$GR3width = 512; // width of GR3 images
$GR3height = 512; // height of GR3 images
while your current Settings.php has
$SITE['GR3DIR'] = '/images';
$SITE['GR3radar'] = 'CCX';
$SITE['GR3type'] = 'cr';
$SITE['GR3img'] = 'jpg';
$SITE['GR3cnt'] = '10';
$SITE['GR3width'] = '512';
$SITE['GR3height'] = '512';
Change Settings.php to have
$SITE['GR3DIR'] = '/images';
$SITE['GR3radar'] = 'kccx';
$SITE['GR3type'] = 'br1';
$SITE['GR3img'] = 'jpg';
$SITE['GR3cnt'] = '10';
$SITE['GR3width'] = '512';
$SITE['GR3height'] = '512';
and it should work in the template.
Remember that $SITE[] values will override local settings in scripts to make it easy to configure using just Settings.php instead of customizing each script individually.
Best regards,
Ken