If you want something made into an AOW, it's best to have a C2 do the paperwork/conversion and pay a $5 transfer. If you, as an individual, do a Form 1 to make an AOW it will cost $200.
If you want to SBR/SBS a firearm you can either have your C2 do the Form2 and conversion or you can do it yourself. the manufacturer (you or the C2) will have to mark the receiver with the appropriate information. You can always do a Form 1 and have the barrel shortened by a gunsmith if it's beyond your capability.
It's been my experience that most individuals that do Form 1's either have a modular firearm to do the conversion (AR-15) or they possess the skill set and tooling to shorten a barrel, etc. like with an AK or FAL.