There are three ways to legally manufacture an SBR.
1) You can apply as the owner and you will have to submit a form 1, submit fingerprints, get your CLEO's signature, etc.
2) You can create a Revokable trust and the Trust will 'own' the SBR and you as 'Trustee' will be authorized to possess and use the SBR. To create a Revocable Trust, purchase a copy of Quicken’s Willmaker at any Walmart; I believe it costs $35 or you can buy it online from
http://www.nolo.com/product.cfm/objectID/6E9ED903-C9B4-42E0-9C2E235DD87A0A8A/309/ for $40. Once you install the software, a wizard will ask you a set of questions and in 10 minutes you have a Trust document. You will most likely name the trust the 'Enter Your Name Here' Revocable Trust and name yourself as the Trustee. Once you have the trust completed, print at least 3 copies and get them all notarized, keep two originals in separate locations and send the 3rd to the ATF with your Form 1 application.
The benefit of a trust is that the Revocable Trust you created is considered by the ATF as the ‘owner’ of the suppressor and as trustee of the trust, you havefull use of the suppressor. Another benefit is the ATF does not require you to submit fingerprints and you can also omit the CLEO signoff. Finally, the form gets approved faster since the ATF does not perform a background check - since you can't check the background of a Trust.
I created a trust after learning about the process on AR15.com and now I have a number of class 3 items.
3) Establish a corporation and the corporation can purchase / make the SBR. Similar to a trust, although you have to pay annual fees to keep the Corp alive. I believe a trust is easier to maintain b/c it's revokable (you can amend it at any time) and there are no fees to keep it alive. However, if you already have a Corporation then this route may be easy.
With regard to securing signoff, it really depends on your CLEO. When I started collecting I was in Holden and my CLEO was very helpful and eventually we were able to get me a green card (we had a few iterations after the state rejected my app since I didn't have a C&R to prove I was a bona fide collector - this was 4 years ago). You always run the risk that you can't get a future signature if you get a new chief which is another reason I went with a Trust.
Also, rest assured the ATF won't be knocking on your door to inspect your paperwork. As stated earlier, it doesn't apply to citizens. You can find more detail and the ATF downloads on AR15.com in the class 3 section (many detailed Q&A threads).
Good luck.