The non-restricted units aren't an issue as i will likely give them to a hunting buddy to hang onto for now along with my ammo stash. But the restricted ones are the main issue here...as I'm not a US citizen and will be down there on a working visa I'm likely going to have to sell them :-(. Well there may be some units on the EE shortly at good prices!
I was in a similar situation when I went down to Cali and the south west for a prolonged contract. It will all depend on the type of Visa you are admitted under. If you are going there with one of the Non-Immigration Visas (L, H1B, O, P, TN or the investor E class), a Form 6 is enough to bring your guns in with you, since the Visa is a
temporary Visa legally speaking (regardless of the fact that some of them can be renewed) and is of a
Non-Immigrant nature; regardless if you have the option (with some of them only) at a later date to apply to change your status from Non-Immigrant to Immigrant (also called "dual intent Visas").
As such, since you will be in the US temporarily (weeks, months, years) and will leave (eventually), you can keep your guns with you in the US for as long as the Visa you used to gain entry into the US is valid. I wrote to the Dept of Justice for an opinion on the matter (I was in the US for almost 6 months on a TN) and got a reply back from them. I can send you a redacted copy for your reference.
However......that's just the Federal laws. Just because bringing my guns into the US was ok with the BATF, USCBP, and USCIS did not mean I was in the clear at the State Level, where they have different rules. IIRC, I only brought 1 rifle and 1 pistol with me into Cali, but the rest of my stay in Az, NM, Texas and NC I had them all with me (AR, Shotty, Rifle, 2 pistols) in addition to small game licenses in each of those states. I wasn't concerned with Cali's laws, as my Canadian pistol mags complied and my bolt action was GTG. I never brought my AR or Shotty into Cali, just to be safe.