@Michael Sears Perhaps you could approach it like you would a deal itself - how much are you willing to take/give up, what would your ideal # be and what would your strike # be? If you didn't partner with him, could you partner with someone else? What would hard money cost you if you did the deal on your own? What are his experience and connections worth to you?
Know what you would be happy with going into the conversation, what your ideal number would be, what you would accept and what would cause you to walk away. It is important to know this going in because you are the most objective now as opposed to when you are in the middle of the negotiation.
50/50 would be good for you considering what he is bringing, so maybe set that as your ideal number and open with it. Justify it with the fact you found the deal, negotiated it and will manage the project. If he accepts, great. If not, know ahead of time where you will walk away.
Goof luck and let us know how the convo goes!