Can you take a rifle and replace the barrel with a shorter one and make it an SBR after approval?
Assuming you already own the gun in question...
Step 1: Go on the ATF website and order a form 1 kit...it will come with all the paperwork you need including the Form 1 Application, fingerprint cards and affidavit.
Step 2: Take the fingerprint cards (you need 2 per application) to your local law enforcement/police department/sheriff's office. Call before you go and ask when they do this (some have specific days and hours--many will not let you just walk in). Also, most places charge a small fee to do it...like $5 per card. So be sure you know that as well and bring cash.
Step 3: Have some passport size photos made 2" x 2" the instructions are on the application. If you don't know how to run a digital camera and print on some card stock have someone else do it. Kinkos/Fedex will do it for $15
Step 4: Figure out the barrel length and the total length of the completed SBR...
Step 5: Fill out the Form 1--there are many many online resources for doing this AND the form itself comes with detailed instructions. Its not intuitive and there are many boxes on the form you will simply leave blank. But again, look at the online resources for this and all will be made clear. There is no longer a requirement to have the Chief LEO in your county approve your application. You just have to fill out the part about LEO notification and ATF will automatically provide notification Having a trust no longer makes much sense because you still have to get fingerprints and photos regardless of Trust or not.
Step 6. Send in the completed form, fingerprint cards, $200 check, photos, and wait.
Step 7. While you are waiting for your form to be approved have your receiver engraved with your name and city/state. There are rules for this in terms of size and depth of lettering and I have found its easier to just send it to someone who specializes in this type of engraving rather than taking it to a trophey shop. You can send rifle receivers USPS Prioriity Mail and I've done it several times with AR receivers using the $5.50 flat rate box. With an AR receiver I have found the front of the Mag Well is about the best place for this as nobody ever sees it.
Step 8: When you finally receive your approved Form 1 you can now legally possess the parts required to assemble the SBR and proceed to build your rifle.