If it is a entire distrib. then you would need to line up #1 cylinder on TDC. the rotor will point at #1 wire, then you can pull it out, and put the new distrib in.
For my former 165 Mercruiser; they supplied a new base plate, electronic module, screws and gapping tool.(plastic) instructions for wiring. Warm the engine before changing the system, as it maybe hard to start with the new parts. It will be needing to be re-timed as it is way behind by 20 degrees or so.