Talk to Rod, but I'm pretty sure the answer is that a trust is not a business and regardless of NFA assets, you can't sell one. As circuits mentioned, even if you come up with some weird scheme to collect cash, you're likely to be in it pretty deep if they catch on. Lots of cases out there where people tried to get creative with ATF/tax laws and got in serious trouble.

Good luck, hope you find an option out there that will work, one way or the other. If some are SBRs, you can disassemble and sell as title 1 guns + parts (separately), without the $200 tax. But be careful and read up on that too, just to be safe.