I just purchased a 20' 1960 boat, that is in excellent condition, and would like to keep it as original as possible. It doesn't have a motor on it yet. I also found a couple old 100hp Mercury outboards, they are listed as early 70's but the picture is of an early 60's motor. One is a short shaft, being sold as running. The other is a long shaft, runs sluggish, being sold as parts. Not being familiar with outboards I have a couple questions. First - can the rotation be changed, so that one can be counter rotated, to use as a pair? And second - What would I need to change the short shaft to a long and are the parts available? Thanks.