I have been out of town and will try to pry as close as possible to the pin and cam pins.....there isn't much room to pry though. The torque will be the last resort.
Well, not quite the last resort. The last resort would be something even more extreme. Maybe filling the brake drum reservoir with penetrating oil followed by lots of hammering on that cam.... and ultimtely followed by using a metal cutting tool to take the cover off in pieces until you can get enough space to get to those brake shoes and make some clearance between them and the brake drum. I've never had to go there, but it's possible that others have.
The problem is that the brake cover is not only a dust and water cover, it is also used for mounting the brake shoe actuating mechanism and the pivots for the brake shoes. So if the shoes have worn grooves into the brake drum and gotten stuck into that expanded position, then there isn't any way to un-expand them. Especially if the springs have rotted away.
And brake service becomes a problem too often because that that cover is not well vented. All in all, that whole brake system design is not well thought out. And that is being generous. Yanmar didn't think through the details of how brakes are used and what happens to them when they get wet. So back in the day when these were under warranty, we always did see a lot of un-necessary rust in the Yanmar springs, brake cam, and drums. It's a problem for gray market machines used in rice paddys too.
Those of us who have had to deal with rusty Yanmar brakes are careful not to let it happen again.
It may cost a cover, but you will get it off, and nice brakes are almost worth the effort.
To avoid another "too soon brake job", lathe the rust pits out of the inside face of the drum, replace the shoes with new bonded ones, use new springs, and make sure water can't enter via the brake cam shaft. Oh, and while you have it off, make up a proper vent for the brake cover. You might want to check if the vent on the axle housing behind the seat needs improving as well.
rScotty