[CA Victoria]

Ditto Mike!
My 2 cents......
Aggressive cleaners will soften some sediment, removing it from the rear of the water jacket could present a challenge without the heads removed. My flathead V8 Block was an older resto not driven much over the last 30 years,
It was treated to a through flush with evaporust product before I bought it. I needed to pull the heads to resolve another issue. I could see stuff in the water jacket so I dropped a magnet down and pulled up a lot of debris. So I flushed it again with the heads and pumps off using with a special long reach tip. I was amazed of how much junk was still trapped in between the cylinders. I started by using a long reach magnet, long screwdriver, and the pressure tip until the water ran clear but still wasn’t satisfied, I was still getting material from the rear with a magnet so I pulled the engine. Allot more material was removed esp from the area around the last two cylinders when I inverted the engine to clean and flush. If not removed this could have ended up in my radiator....I’m using Gano filters just in case!