Well, if the aircraft's engine parameters are correctly placed, you can just copy the figures and paste them into the smokesystem entires.  I think . . .

If not, estimate the position of each engine and fiddle with the entries until you get the smoke in the correct position.  I believe the first number is the distance outboard (lateral) position and the second is the vertical position.

NOTE: for some reason, FS doesn't allow you to edit the longitude of the smoke in the aircraft.cfg file.  To edit this, you must edit the smoke file itself.  This shouldn't be a problem with most aircraft, as the position is about right.