The trigger *should* have been the upgraded "enhanced" trigger with a 5K serial number unless it was built from old parts.
That said, as far as braces go, IMO, the best brace for the XCR is the RA/Gear Head Works collaboration for the Tailhook. They have a new model that just dropped call the Mod 1C (the old one is a Mod 1). It's even smaller and folds even tighter. I'd be surprised if RA doesn't go to this as the default Tailhook on their brace once it's in full production mode.
The problem is the expense....they are about $300 IIRC...with the old Mod 1 Tailhook. The new 1C is slightly more expensive.
A light weight option is the AR adapter from RA with a Shockwave Blade and tube, but that option doesn't fold...but is much cheaper; around $100.
I'd do a ambi mag release too ...if those are still available for your older model lower.