Re: How do I lower the lower unit on i/o?
on that age of mercruiser, you probably have a either a 3 button panel on the dash, or maybe even a couple of toggle switches. There will be a "trim" button/switch and a "trailer" button/switch. If buttons, they may share a common "down" button. Once you lower it all the way down, the "trim" button/switch is used to adjust the trim while under way. If the sensors still work, it will limit the amount that you can lift up the L.U. while under way (to avoid an unsafe level of bow lift). If you want to lift it higher to come into shore, or put on trailer, use the "trailer" to go the rest of the way up. Try and avoid running the engine when it is tilted all the way up. It's hard on the U-joints (even when the LU is shifted into neutral).
If it hasn't been run in a while b/c of the motor problems, you may consider splitting the lower unit to replace the rubber impeller that supplies the cooling water to the engine (like outboards have). Old ones can be brittle and break. It'd be a shame to toast the motor you just fixed. You might want to just pull the lower unit and grease/inspect the U-joints and gimble bearing while you've gone this far. Greasing U-joints requires pulling the LU from the boat, and is supposed to be an annual thing. Seems tough at first, but I can remove/grease/replace mine in under an hour now that I've done it a few times.
Look in the "adults only" of the mercruiser forum for tons of good info that you need.