How can I saddle myself as a Marketing Manager?

I was offered an opportunity by a client who owns a successful tire shop. It all started when I took him out to lunch and jokingly asked him to hire me as his Marketing Manger to help him increase sales. Said I could go out and make deals with local dealerships and help finally make 1M in sales. He was really open to the idea and asked me if I was serious. My question is, those with experience, how can i put together a detailed proposal detailing how I can help him. What can I add to help me land this.

EDIT: misspelled title Sale* myself

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