Former boat shop owner and Mercruiser/ Mariner dealer.
Never quote without a teardown.
ALWAYS add to any estimate that it is 'not withstanding any difficulties in disassembly'.
Having used the Merc flat rate manual, always add AT LEAST 50% to the times quoted. Those times are for an experienced, factory trained technician to do the job on an engine (or drive) on a stand, new (with no corrosion) and with all the special tools at hand. He's also doing it every day, and knows EXACTLY what to do, without even having to look at the manual. They are unrealistic in the real world.
Chris........