Outsourcing a portion of code

I am working on an application in which requirements came in that require me to refactor some of the code. The task is not that difficult, essentially breaking up a model into 2 models then making sure everything points to the correct model.

Unfortunately, this model is the primary model for the entire application. Which means to do what needs to be done would take about 6-8 weeks. I thought perhaps I could outsource this portion to allow me time to work on other needs.

Does anyone have any advise on outsourcing work? I plan to allocate some time to review all their changes and to test, but my hopes would be to get the dev time down to about a week, if not a little quicker.