Find The Word


I am a word of 12 letters. 

My 12, 4, 7, 2, 5 is an Eastern beast of burden. 

My 1, 8, 10, 9 is a street made famous by Sinclair Lewis. 

My 11, 3, 6 is past. 

My whole is a person suffering from delusions of greatness. 

What word am I?
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Answer:
Megalomaniac.

(And the words are Camel, Main, and Ago.)