I wouldn't replace the coupler unless there is a reason to do so, IE: the splines being worn, pointy or uneven hills/valleys. I would rather have 100% perfect engine alignment with a good used coupler, opposed to having terrible alignment with a brand new coupler that could strip out quickly. My old coupler was V'ed out due to poor alignment, so I replaced it with a good used coupler, saved $100.
Along with things everyone mentioned, I'd replace the bilge pump hoses if they are the cheap corrugated stuff. Anything that penetrates through the fiberglass and into the deck and stringers needs to be sealed with 3M 4200 or 5200.
Actually....... Now is a great time to check the condition of the hull and see if the boat is worth a new engine. On my last boat I had rebuilt the engine and was getting ready to put it back in when I got the wild idea to check the deck and stringers. That old 72 SeaSwirl got a trip down to the landfill as it wasn't worth rebuilding the deck and stringers.