I have a 90 3.9 V6 (basically a318 with the back 2 cylinders cut off) and a 91 3.9. Both use an LA 318 timing chain cover and neither have an opening in the cover for a fuel pump. Mopar 318 & 3.9 V6 have had an electric fuel pump since 1989. The opening in the timing cover for the fuel pump went away during 1989 as the supply for the older covers with the fuel pump mounting got used up. Some early 89 motors has the pump mounting, but by the end of the year it was gone.

BTW, the 91 3.9 I have still had the old pulley system on it. That might suggest that the change over to the serpentine belt was a simple bolt on process, or it could mean that all the 318s got the serpentine belt and all the 3.9s got the old stuff until it was used up, or the 91 model year ended.