Clackamas Co. is also no problem, as friends living there have said.
You of course have to have your forms all filled out (2 copies) first before going in with the transferors signature and the weapon information as well as yours including a 2x2 forward facing mug shot of you.
I would call the CWP office of the sheriff dept. (look up in yellow pages) and ask if you can make an appointment for an NFA sign-off and to get finger printed (if you called the wrong dept, they'll get you to the right place). While getting the prints, I would at least one extra set, depending on how many NFA toys you plan on getting in the next year.
You'll talk to a secretary, most likely, and they will make the appointment for the deputy and finger printing. You'll go in, pay a small fee for the prints, get printed and then see the deputy for signature. You of course have to have your forms all filled out first before going in.
Remember, it is not the CLEO to say you may or may not have the NFA item, only that there are no laws against the citizens of the CLEO's jurisdiction (where you live) from having them. The fed. gov't (FBI) does the background investigation (with the fingerprints you provide) on you to make sure you're honest Abe.
The deputy may as a few questions about the NFA item but in the end, he's probably just curios. I've also heard some counties don't sign on the spot.
You may have to mail them in and then they'll sign and mail back so be prepared for that, should it happen... which add time to the process.
It's really not difficult at all. The hardest part is 'pending' while the NFA slowly does their thing.