Gentlemen,
From Mr. Richard Cavicke, Chairman JCNA JCRC, comes the following (from an off-forum email exchange in the past couple of days - copied/pasted here with his permission):
"For the past 50 years, very interested XK120 owners and Judges have been unable to find any official Jaguar Cars Ltd. publication that confirms the production positioning of the front parking light/turn-signal, red jewels. The following references represent the best information available based on documented photos and observation of original XK120's.
This issue has been pretty well researched and, at least for the 120, no official information has been found to support any conclusion other than the fact that the vertical end of the tell-tale/jewel goes FORWARD.
Here are three take-it-or-leave-it references:
- The 1998 Denver CO, AGM Second Edition of the XK120 Seminar Bulletin, paragraph 7, page 62:
"The red "Jewel" indicator on the top of the running (parking lights) should have the high side toward the front of the car."
- Porter's New Edition of Original Jaguar XK, page 87, has a photo of the lamp and jewel with the comment:
"In spite of much debate and conflicting evidence, it is believed that the small red tell-tale should be mounted this way round, with the vertical face to the front."
- Viart's XK120 Explored: Page 299 has a drawing of the lamp and jewel with the comment:"Visual Indicator, Red Plastic, (Lucas 573449), Vertical side forward secured to casing by C.4098/2 Spring Clip."
(- Related - George Jones', JCNA Mark 2 Judging Guide: Page 12, "Exterior, Tell Tale (front parking light) "Red plastic. The correct orientation for this is with the long slope (tapered portion) towards the rear of the car for MK 2's, and towards the front for the 240 and 340 cars." Supporting information is attributed to Steve Kennedy's The Classic Marque, p.115. and his associated research.)
Official Jaguar XK120 publications sadly lack any close-up photos or detailed drawings of the lamp and its jewel. Unless some contrary "official" evidence is found, or JCNA wants to establish its own different "standard", "Flat Forward" is currently considered authentic for the XK120.
This may not be the "final" answer, but it's the best one we've got in 2014."
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Thank you very much to Mr. Cavicke for chiming in with these references, and for providing what we hope is a "final" (for now) answer.