[tubman]

That looks pretty bad, but you could try. I like a chelation agent (such as Evaporust), but I agree that it is expensive, For situations like this, I use a product called Rust-911, which is a concentrate and is significantly cheaper. When I did the '51 Merc in my Ford club coupe, I treated it with a commercial product first and then flushed it with plain water. I then introduced the Rust-911 solution and let it sit a day. I then drained, treated, and flushed the system a second time, and repeated the Rust-911 process a second time. I then did a final flush and rinse. Here's how it came out: