James, I'm liking your approach to this and it sounds more encouraging that you're up for the task and not a novice.

Again the OMC and the Mercruiser are the same engines that you'd find in a comparable 3/4 ton Chevy pickup with the exception of a different cam shaft, steel stead of cast iron crankshaft. The freeze plugs are a non corrosive metal due to usually a raw water application as well as the water pump. The diffrence between an auto and a marine pump is the boat pump has special sealed bearings and usually powder coated inside to prevent water damage to the bearings and also prevent rust corrosion. The alternators and starters have spark resistant shielding as well. If a guy is handy with tools you shouldn't have any problem with maintainance.
If you decide to persue. this project. It'd be worth getting a mercruiser shop manual. The book is extremely thourough and great to have around. You can get a complete shop manual for 20 -30 bucks on eBay.
Keep us informed. Btw there's a lot of great archives in rec boats that a person can look up as well.