what your saying is confusing. the upper body line is there if it is from grant customs. maybe some pics will help.
here is the hole after the tail light is removed (the gold stuff is weld through primer)
the filler, that must be trimmed to fit, all bodies are slightly different.
you will have to fab a small filler piece in each side
fit and weld, see the upper body line, needs grinding, but it's there
make a new hole and insert light