[Blue197320]

fr.frank, if u do not mind i have to go against something u mentioned about the mercury water pressure. u said at WOT it should be at 18-40 psi. all the info i have heard that after the poppet opens (about 3k rpm) the pressure should drop to about 8-12 psi and stay there all the way thru WOT. maybe im wrong but that is what ive read on s&f and the local mechanic said the same thing. no disrespect at all.

ABSOLUTELY change the poppet and thermostats!!!!
You need to change out ALL water lines/hoses as well, including the telltale hose (pisser)

If you're serious, temp gauges should be on each cylinder bank, with the sending units at the top. Keep the pressure gauge. Older pre-99 Merc V6's require 8 lbs of pressure at idle to prevent overheating and steamlock, and 18-40 lbs at WOT.

Muddy, any Mercury control box from from 1968 through 2002 will work. The Mercury cable system was unchanged throughout those years. FYI, All analog control boxes from 2003-2008 will work as well. You just can't use the digital SmartCraft controls.