I can't help you with "exact measurements" But the bumperettes on the rear on my 65,66 and 64 were centered exactly on the trunk line on all 3. the center of the bumperette was on the line of the trunk on all 3 cars. here are a few picture that I snagged to help a little
sorry they are all 66's, but that's what I'm currently working on:D
nothing was found in the factory service manual about placement. and none of my bumpers have the hole for locating the bumperettes that I have that came in the trunk of the 66 dart.
