Contributing to the discussion (albeit very old):
'69 Baltimore-built SS396 Chevelle Convertible
Trim Tag:
<span style="font-family: 'Courier New'">
BODY BY FISHER 2
ST 69 13667 BAL121651 BDY
TR 791 51 A PNT
10D L048813
</span>
The 10D is consistent with the NCRS shipping report of 10/28/1968 assembly start.
The L is consistent with the car being an SS396, and the 'fossil find photos' showing all visible SS396 indicators on the car, including:
<ul style="list-style-type: disc">[*] SS396 emblem and blacked-out rear cove (body pierced)[*] SS396 emblems on front fenders, behind wheels (body pierced)[*] SS396 emblem on front grille[*] SS396 emblems on interior door panels[*] Black painted headlamp bezels, deluxe tail lamp bezels, polished trim bezels on front parking lights, and front side marker lamp bezels without engine displacement.[*] Styled 5-spoke SS wheels[/list]
The 813 matches the inspection sequence on the car's IBM punch card.
Only thing left to decode on the TT is the 0-4-8 in between the "L" and the "813"