The way I've checked lateral balance is to make sure the wings balance. I find and mark the center of the wing tube, place the wings on the tube, tie a string around the tube at the center mark and lift the wings by the string. Add weight to the light tip if the wing is covered already, or remove weight from the tip of the heavier wing if it's not covered yet.

I think the offset of the engine, being so close to the center line, will have negligible effect on the lateral balance. If you are concerned about this, how about attaching a string to the engine mount at the center of the firewall and lifting the whole plane by it and the tail?