Just to clarify (and I think you know the laws and just didn’t type what you were thinking.
The barrel length is 16", while the OAL is 26".
A couple things to support the explanation. First, from the ATF’s SBR FAQ:
[i]Q: If I remove the short barrel from the registered SBR or SBS, is the receiver still subject to NFA transfer and possession regulations?
If the possessor retains control over the barrel or other parts required to assemble the SBR or SBS, the firearm would still be subject to NFA transfer and possession regulations. ATF recommends contacting State law enforcement officials to ensure compliance with state and local law.
Q: Does the installation of a barrel over 16 inches in length (SBR) or 18 inches in length (SBS) remove the firearm from the purview of the NFA? If so, is this considered a permanent change?
Installation of a barrel greater than 16 inches in length (SBR) or 18 inches in length (SBS) will remove the firearm from the purview of the NFA provided the registrant does not maintain control over the parts necessary to reconfigure the firearm as a SBR or SBS.
Q: If I remove the short barrel from my SBR or SBS, may I move the firearm across state lines without the submission of ATF Form 5320.20, Application to Transport or to Temporarily Export Certain Firearms?
If the registrant retains control over the parts required to assemble the SBR or SBS, the firearm is still be subject to all requirements of the NFA. ATF recommends contacting law enforcement officials in the destination state to ensure compliance with state and local law.
Q: May the short barrel on an SBR or SBS be replaced with a long barrel for hunting or other purposes, with the intent of replacing the short barrel?
Yes, and you will not be required to again register the firearm before replacing the short barrel. ATF recommends written notification to the NFA Branch when a firearm’s configuration is permanently changed or removed from the purview of the NFA.[/i]
The “maintains possession of” often raises a question as to what that means. The best answer I’ve seen on it came from one of the ATF letters:

So…hope that helps. You’re definitely in the clear as far as NFA/non-NFA is concerned. It’s only an SBR when configured as such, unless you have all the parts and no other legal way to use them
Q: May a FFL or an individual legally possess the parts to manufacture an SBR or SBS as long as no firearms are actually assembled?
A FFL (Type-7 or Type-10) who pays the Special Occupational Tax (SOT) may possess parts required to assemble NFA firearms. A non-licensee or FFL who has not paid the SOT is required to register any NFA firearm via an ATF Form 1 (5320.1) prior to acquisition of the parts required to assemble such firearm.