I would book this as a connection, knowing that the late-delivering carrier would rebook me the next day and provide a hotel and meals. In your case, it is a matter of risk tolerance. A new WN ticket at walk-up prices runs $200-300 on this route. If that plus the cost of a hotel and a few meals is too much to risk, I would not book the last flight out. If you can sustain the risk, then go ahead and book.

My general advice is that transfers across tickets should have 2-3 times the MCT and preferably an overnight. You don't have that, so I wouldn't recommend it. You may well make it, but the risk is 100% yours. If there are delays at CBP or if you have any immigration issues, this transfer will not work at all.