I appreciate all the responses so far 
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I deliberately left my original post a bit vague in the hopes of getting as much breadth and depth of responses as possible, in the hopes of seeing some angles I hadn’t considered, and got some, so thanks! That being said, I should probably clarify a few things:
-I am quite familiar with the boating hobby, so the advice on expense of boats/speed/rules of the road is probably unnecessary. But I know you guys are just looking out for a fellow GRMer, and I appreciate it. As mentioned, I got my first boat at 12, and have been on board boats (both power and sail) since my second day on earth. Additionally, I’ve taken Marine Navigation courtesy of the Navy’s ROTC program in college (as an outside student), drove a race committee boat for offshore sailboat racing as a summer job (and logged about ¾ of the hours needed for my Captain’s license), as well as helped run a commercial marina for 3 years. So not my first rodeo, more of a return after a 10+ year hiatus. Any cool technology in the last 10 years that people want to suggest, I’m all ears! Though PODS or Zeiss drives are out of my budget.
-To clarify the intended boat and mission, I am looking at “Fast Cruisers”. Something that will cruise on plane at 20-25 knots, max out at 35-40, sleep 4-6 people in relative comfort, and have a small galley and head/shower. The intent would be to take a gf + occasional other couples for weekend trips, sleeping on board. I have a few specific models in mind, but most of the boats in this class came with twin 350/Alpha drives or 454/Bravo drives for propulsion. I am currently torn between picking up a fairly good condition boat for $15-20K and using it for a few years, with an eye towards this upgrade later, or spending $5-10K on a good hull/interior that needs engine/drive work already, and going ahead with the swap now. Which leads to….
-My goals for the swap aren’t to turn a small runabout into a cigarette boat, which may be what some folks were envisioning. The LS1s would fall between the stock small blocks and big blocks in power, but would obviously do better on power/weight. The big benefit that I would hope for would be a large boost in fuel economy due to EFI/torque/weight down, with similar cruise speed. Some smaller boats that have done similar conversions claim almost double the mpg (admittedly we are talking going from 1 to 2mpg), though I’m sure it is a combo of the EFI/tuning and the weight, with possible user optimism (wait…I mean prop optimization, yeah that’s it) thrown in.
-Regarding engine speed, cruise power would hopefully fall near the current engine speeds of 2700-3200rpm, which I would think is within a gas engine’s range for sustainable operation. I did consider diesels, and some have done 4 or 6 cylinder swaps, but that may be a bigger undertaking than I am willing to deal with. The benefit I saw to the LS1’s is they could be made to work with the existing mounts/drives/fuel system with adaptor parts, whereas the diesels are going to be pretty much clean slate.
-The engines would absolutely have closed cooling systems, that’s a good idea on any engine that sees salt water. I was more asking if anyone had heard of beefing up the anodes or adding additional galvanic corrosion points, or if there were any additional marinization concerns with LS1s beyond the normal backfire arrestors, water cooler exhausts, sealed starter/alternator, ignition/ECU, etc……the aluminum head/block worries me for no reason I can put my finger on.
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