Without a schematic, unless you can find one, it looks like all the vital spark components are on the half of the board that is close to the connectors. The IC (Integrated Circuit) components look like they are dedicated to additional functionality on the Bros 400 also a guess that extra 1 connection is headed for the tachometer on the NT.
Have you done any meter testing for resistance values on the new box that relate to the specs on the old one? We are looking for similarities as per your RC17 service manual inspection of the original spark unit. You're going to need a multi-meter at the very least.
... any reason you want to use this particular off model spark unit, or is it just what you have on hand?
and this site is generous enough to support them.
