Gramps is right.
The second digit for the product numbers of locomotives and sets from 1970-1986 was usually the year it was first produced.
The 6-8490 Lionel Lines Trolley was originally scheduled to be part of a stillborn 1984 Fall Collectors Center package which was canceled largely due to the product delays experienced with the move to Mexico. Several other products had their dates and subsequently product numbers shifted during this time.
It was 1986 when the Trolley made its first official appearance, with the number 8690. But many of its component parts retained the original number, including the end window strip where the 8490 is clearly visible.
TRW