how to clean cox engines and make make them look like chrome?

It's very possible.

However, it takes time. If you want to restore that Pee Wee it's going to take some effort.

Many methods to be found on the forum using a search. Most (if not all) are very effective.

Your Pee Wee is very corroded so it will take some light wet sanding to get back to base metal where you can polish. I use Mothers, but there are numerous aluminum polishes available.

The backplate may come around with Brasso, but if the plating is worn away, then you can't do much about it.

Cylinders can be re-blued and head can be chucked in a drill and sanded clean. Fins can be straightened, but will never be as new again.

In short, do a search and find what will work best for you with the tools you have available.

Ron