First round of issues found on the 63 Valiant

If the crud is in the engine, under the valve cover. It would be best to use a small wire brush and shop vacuum to remove. If this is correct, DO NOT FLUSH the trash loose, unless you need replacement anyway. If really bad the only way to remove it is to remove engine and put on a engine stand and clean it that way. Head would need to be vatted to clear oil passages and it would not hurt to hot tank the block also to remove rust scales behind the freeze plugs.

If you do flush out the oil, the oil pump screen will clog. Co-worker had these issues and when the fuel pump leaked gas into the oil the trash moved and motor stopped. He was real bad about not changing is oil, to save money.