I'll tell you what I did, but no-one will like it.

I replaced the water pump. When I had it off, I stuck a garden hose in one water pump hole and turned it on until it ran out completely clear. Then I pulled a heater hose and did the same thing.

It's not going to remove the scaling that a chemical flush will, but I know that there isn't any alkaline flush crap left in my system either.

By the way, Prestone makes a really good chemical flush. It's 2 parts. The first is the flush chemical. The second part is the neutralizer for the flush. It cleans EVERYTHING from the inside of the block. Sometimes leaks develop that hadn't shown up before as a result of this flush. These leaks are almost always because dried coolant crystals and sludge were plugging the leak.