Standard Motor Products AC423 Idle Air Control Valve is the nonn- Mercury IAC part and is $43.00 on Amazon. I carry a spare and correct allen wrench size.
DO it
I had my boat in high n dry storage and it was great.
Boat in on lift behind my house now and frankly it was easier to clean and "deal" with the boat when at high and dry facility
I use a product called "Iron Out" a little less aggressive than Hull cleaner.
Works for me on "stain" mix in a gallon pressure sprayer spray on and rinse off after a couple minutes.
I use this style pump sprayer and use about 1/2 the product vs. using a squeeze trigger bottle.
https://smile.amazon.com/Solo-418-One-Hand-Pressure-Sprayer/dp/B000BX4VXI/ref=sr_1_3?ie=UTF8&qid=1487857265&sr=8-3&keywords=pump+sprayer