I wonder if someone who is better with computers than I am could come up with something like Sheldom Browns Gear Calculator for determining chainline for various width BBshells, E bike motor kits and chainring offsets. It might be a good sales/shopping tool if you could determine your existing chainline and then order parts that will duplicate that for you.
Input BB width,motor kit and width, and then enter several offset chainrings or adapters to see which comes closest to what's required.
Maybe even how much they can be shimmed and which direction. Like "55mm (+4mm)".