The inside of the block is pretty crusty.

I took a piece of coat hanger and used it to scrape/loosen big chunks by poking down through all the coolant ports in the deck surface.  Then used the shop vac to suck out the big bits.

Made a block off plate for the water pump port on the front of the block.

Then filled the block with Metal Rescue for an overnight soak.

This stuff is a mild acid/chelating agent that attracts the iron oxide molecules away from the cast iron without being strong enough to damage the underlying cast iron.  After I drain it through the block drain, I’ll fill it with some water for a rinse and then put some anti-freeze in it until I’m ready to assemble.

And here’s the front cylinder – essentially rust-free.

Drained, filled with a mix of water and antifreeze and let sit for a bit.  Then put the block drain fitting back in.  Ready to move on!