I'll take a shot at this...
1) First, he needs to be sure all the items he's moving are legal in the state he's moving to - not all Class 3/NFA stuff is legal in all 50 states, and even among the states that do allow C3 some don't allow SBSs, some do. One source to check is :
or call the BATF.
If the weapons are OK to transfer, get a few 5320.20 forms
Application to Transport Interstate or to Temporarily Export Certain National Firearms Act (NFA) Firearms
ATF Distribution Center
P.O. Box 5950
Follow the instructions.
I'm not sure of. I've heard you can fax the forms in and that's all you need to do, but I'd sure call the ATF and be sure - or someone who's done it will post. I've heard it doesn't take long, a couple of weeks...?
3. The Class 3 items must remain under the control of who they are registered to. If it's your boss, he has to take them there. If they are registered to your boss' corporation, a corporate officer can be designated to take physical possession of them during the trip. Unless your boss is a SOT (he'll know) he cannot ship the items, and I'm not sure he could ship them to himself like that anyway.
4. If C3 items are not in the possession of the registered owner - or in the case of a corporation, a designated officer - then that could be considered an illegal transfer. This is the case regardless of whether you're moving the guns to a different state or to the shooting range.
Have fun and good luck.
BTW - does he let you play with his C3 toys? What kind of stuff does he have? Not being too nosy, just curious