Are these sentences natural? Or how would you say it?
A man is a man as good as he keeps his word.
A man is a man as long as he keeps his word.

Question

Are these sentences natural? Or how would you say it?
A man is a man as good as he keeps his word. 
A man is a man as long as he keeps his word.

Answer

I would personally use "A man is a man as long as he keeps his word." I would say it sounds more natural and it rolls off the tongue better.

Answer

I think this sentiment is most usually expressed as 'a man is only as good as his word" - or you can leave out the 'only' and say 'a man is as good as his word'.