(a) even used (b) used even
In this sentence even is an adverb (meaning it is a word modifying, affecting, influencing a verb)–and in this way–even is used for emphasis. We should usually put an adverb or other modifying words before the word or words they modify–before the verb (NOT after). We are stressing how differently Buzz Aldrin used something–in this case a pen; we are not stressing the pen, even though the pen is the unusual tool used in this story. To emphasize that (the pen, itself), we can change our intonation and say pen!