the chamfer should be about 1/2 mm in length from flat surface to surface on all your ports, as much of a radius as possible. the point is to make the cylinder port surfaces (lines) straight, like they intended, not jagged. (unless doing eyebrows or other fun stuff) think smooth, clean lines and if it's sharp running your finger of the port, then a ring is more likely to catch.
i'll also agree that bridge should be fine since it still has a solid MM left unmarred, at least chamfer it. if it makes you uneasy definitely grind it into a straight skinny bridge to look more like || than |\ and it will still serve its purpose. definitely one of the uglier castings ive seen!