Flip/Gut deal with GC (Boston)

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The deal is as follows:

350k total cost to rehab 3 premium units in the Boston market that will rent out around 2.5k a unit. Cash is tight so I offered to put in 160k upfront and at the end I refinance the home and pay him the remaining balance. I made it clear that he cannot put a mechanical lien on that property as that would prevent me from refi. He will also be responsible for all the subcontractors so they can’t do the same.

Putting a document together with my attorney on the terms and he will have his look over it and we sign contracts just Incase..

Has anyone done this before? Does it sound alarming? Do you recommend? Is there anything that else that could prevent the refi from happening?

Thoughts?