Below is from the 747 maintenance manual (Before you ask, YES, I checked both the 747 Classic and the 747-400, they're both the same)
(5) Nacelle abbreviations
Nac BL Nacelle Buttock Line. Nacelle Buttock Line 0.0 for
inboard engines is 2 degrees inboard from Wing Buttock
Line 470.0.
Nacelle Buttock Line 0.0 for the
outboard engines is 2 degrees inboard
from Wing Buttock Line 834.0.
767 engines are angled inboard 1 degree.