Need more info. If it is an '86 m/t it is an AMC20. One year deal. As to gearing that mainly depends on your engine tranny combo. "Metric ton" alone tells us almost nothing. An '88 4.0/auto will be 3.55 regardless of the rear springs for example
Fish plate?
In VERY simple terms think of it as running a large washer under a bolt head to distribute the load. It is a plate placed over a repaired area or one subject to exta stress to spread the load
I personally would not clean that line and trust it, either. To each their own. I bent all new lines for mine and it really wasn't to bad in effort and cost Just duplicate the original
I know pictures of the various points would be helpful for people reading this thread later. My google-fu must be weak today as I cannot turn up anything on this from prior posts.