Paul,
Replacing a radiator on a 300E is not too bad a job. I have done it several times.
I would highly suggest that you make sure your new replacement has the metal reinforced upper neck.
I used the search button above and created these links for you using the key words: 300E radiator replace
300e radiator replace
As an FYI, typing in caps is considered yelling.
Keep us posted,
Haasman