Just changed our starter today. What a headache! On boat in our signature, there's no "engine room" by any description. Has a motor box like an inboard speedboat except back at the transom. (DeeVee, you in there, brother? If you've got to change one, allow half a day.) Anyhow, a couple points you may find helpful:
1. Be SURE the starter mounts with the MerC bolts!!! Auto supply bolts will hold the starter in place OK, but MerC furnishes them with a 1/2" hex head (cars use 9/16") that's also extra "tall" (longer hex surfaces) compared to automotive. In the staggered bolt pattern, one bolt is right against the flywheel housing cover. Even still, unless there's room for a 1/2" thin deep socket, standard socket won't leave clearance for the head of a ratchet. I ended up loosening and tightening with a short 1/2" x 9/16" 12-point box wrench from the day Craftsman had mechanic-quality hand tools with VERY thin walls.
2. The replacement starter had TWO nuts on the battery terminal stud. That's the way Delco-Remy used to be, so I tightened the second nut tight to the back of the solenoid cover. Much later in the job I found all my terminals wouldn't fit. Turned out the extra nut was not needed. Solenoid is made with a special washer that holds the stud in place, where Delco-Remy had used a nut. Simply removing the extra nut allowed me to continue with the connections.
3. I'm getting too old for this!