Pulling a powerhead is not as big a job as it may sound. Jeff's method is sound.
I pull them (somewhat) regularly on the small motors (25 horse and under) that I more typically work on. I usually find a paint scraper tapped around the edge of the base helps get a "stuck" powerhead to separate from the exhaust base. If you pull the powerhead you will minimally need a base gasket and then depending on how much you take apart from there, perhaps a driveshaft housing gasket and the seal that goes around the exhaust plate.
Before I went the route of pulling the powerhead, and you may well have to do it, I would first try and remove the water tube from the "bottom end".
Remove the lower unit, tilt the motor up as far as you can and take a look up the leg.
The water tube is only fastened to the plate up there by one screw (a clip with a seal fasten the tube to a grommet in the plate).
You "might" be able to get at it with one of those uber-long screwdrivers that places like Harbor Freight sells for a few bucks. If you can get at it that way, while tedious, it may be a whole lot less work than pulling the powerhead.
Worth a look...
And Jeff must be getting soft - I pulled the powerhead on my 140 all by myself without a hoist - with the flywheel removed it couldn't have weighed more than 100 pounds or so
