DDK - Die Deutschen Klassiker

Where can I purchase the full chassis strengthening kit for the 914 and how much do they cost?

Try the 'Engman kit'

any particular reason that you want the strengthening pieces? The factory fitted them to the race cars but don't recall ever seeing them as a factory option???

To be honest they are very easy to fabricate - as I recall the old man knocked up a set for me in about half an hour.