How to clean gunk out of new build

I've replaced a quart of oil with a quart of Marvels Mystery oil and run for a whole oil change. All kinda crap came out. I also did this to my 64 Valiant I got in January. I only left it in for about three weeks, but again, it cleaned it out good. As long as you don't race it like that or romp on it hard.......just drive it like an old man and it'll be fine. That stuff really works.