I took some pictures of mine with/without decklid letters.Had to be a close up shot so you need to judge using the trunk lock as a guide("T" lower hole is not exactly center of the trunk lock) from these pics.I realize you are pressed for time and this may help you a bit if you study the pics and should get you close to what you need in a pinch.Either that or hold off on the paint.Goodluck and have a look.
David
http://FirstGenFirebird.org/show/closeup.mv?CarID=571 If i don't get this car back on the road soon i'm gonna go postal! On a quest for FGF knowledge 1968 Pontiac Firebird Convertible 1969 Oldsmobile Cutlass "S" Convertible *Sold*