A PCR is first and foremost a PISTOL. That being said it needs to be less than 26" long and have a barrel less than 16" long both of which you have. Here are two of the finer points to which you may be inquiring.
Attaching a FOLDING BRACE, FIXED BRACE or COLLAPSIBLE BRACE to the 1913 rail on the back WILL not increase the length of your pistol as it is considered an accessory. There is an ATFE letter out there describing how that works, get a copy of it.
If you install a non folding brace or anything else the length of pull (the distance between the rear most portion of the brace and the forward most portion of the trigger) “is recommended to be” less than 13.5" according to a letter from the ATFE to a Mr. Gaetz (get a copy of this letter too) otherwise the length of the brace will be considered a “stock” which makes it an SBR. If you have ape arms you might could argue the length but it would be exceedingly expensive.
Any “brace” that is approved for use on a pistol is pretty much required to go before the ATFE inquisitors and as such any brace you wish to put on your pistol should have a qualifying letter from the ATFE. I bring this up simply because I was involved in a “passionate” discussion with a VA State Trooper regarding a MagPul AFG which he said had avertical end and therefore constituted a vertical fore grip. The rear of which is not vertical but the front nub is vertical. I had in my pistol hard case a copy of the ATFE letter stating that the MagPul and similar were considered AFG’s (Angled Fore Grips) and NOT VERTICAL The Trooper was all hot and bothered to confiscate my pistol and put me in cuffs. Me being me, I happened to know the State Trooper firearms bubba and called him in the presence of the young Trooper. The matter was resolved rather quickly with the State firearms bubba quoting page and verse and the young Trooper saying “Yessir, Yessir, Nossir, Yessir, I understand Sir.”
My time was taken and it was a bit disturbing but another young Trooper was better educated and I am told there will be “Mandatory” training at the deck plate level about such things as the legal bills would have cost the State plenty.