Probably none of the liquids will work or at least fully clean the salt. I had a Yamaha, which had apparently not been flushed. We ended up pulling the head, using tools to work out the salt deposit--same down into the passages. Then using Hydrochloric acid got most of the rest of the salt and scale out.
Starbrite makes an engine descaling liquid. Vinegar may work to some degree. If it is starting to overheat--I would at the minimum pull the head to see what degree the passages were clogged.
200 HP--is a great motor for the C Dory 25, and that is what I would put on the boat, if I had an excuse to change out motors--not likely, with about 500 hours and running very well!
Tom on C Otter had a 200 HP 6 cyl Yahama, and traded it out for the 200 HP 4 cylinder motor. Hopefully he will give you his opinion. The 4 cyl is 487# for a 20" shaft basic outboard. The V6 F200 is 608#, so there is a weight difference of a bit over 100#. The V6 is the same block as the 250, and it is 3.6 L displacement, so a lot more "reserve".....vs the 2.8 Liter displacement of the Yamaha 200 4 cyl.
We run a lot of weight in out boats (extra batteries, freezer, etc) and although the boat does better with lighter weight--faster and better mileage, it "works" with the weight and a 150. I do recommend that one put a Permatrim on the motor--this gets the bow down more, and a better ride in the chop. Do you, or will you put a Permatrim on a new motor?
There is the cost of re-rigging--assuming that you can use the Honda gauges and binnacle, should work on the Tohatsu?