In any contract for financial assistance with the federal government the authority may obligate itself (which obligation shall be specifically enforceable and shall not constitute a mortgage, notwithstanding any other laws) to convey to the federal government possessions of or title to the redevelopment project and land therein to which such contract relates which is owned by the authority, upon the occurrence of a substantial default (as defined in such contract) with respect to the covenants or conditions to which the authority is subject; such contract may further provide that in case of such conveyance, the federal government may complete, operate, manage, lease, convey or otherwise deal with the redevelopment project in accordance with the terms of such contract: Provided, That the contract requires that, as soon as practicable after the federal government is satisfied that all defaults with respect to the redevelopment project have been cured and that the redevelopment project will thereafter be operated in accordance with the terms of the contract, the federal government shall reconvey to the authority the redevelopment project as then constituted.