1988 searay sundancer drive help

[bobbynj66]

I have a 1988 sea ray sundancer twin 4.3 mercs I need to know how to find the gear ratio and also how hard is it to put the new upper housings together with my lowers is this something I can do without alot of difficulty I am mechanically inclined to my own brakes have owned tractors trailers and dump trucks have always done my own work but dont know much about boats thanks for any help Bob