I have seen lots of non US citizens owning N reg.
Are you sure?
Really sure?
Because I have to agree with IO and others; foreign nationals, unless resident, are not normally permitted ownership of an N-registered aircraft. Normally, they are owned by a US-registered Trust Company, of which the 'owner' that you see is a benefactor.
That's certainly how it works with the N-registered aircraft that I fly.
Previously, you also said that the aircraft is already N-registered and that you won't be re-registering it. Bear in mind that FAA Certificates of Registration are issued with the registrant's name and address. In other words, if you buy it, you must re-register it, even if you use the same tail number.
That's how I understand it. E&OE, of course.