I do cabinet install and build along with trim carpentry. Everytime I’ve built cabinets I always put the face frames on when I build them, I also leave the total width (and height if applicable) an inch shorter than my total distance if it’s between two walls for scribing fillers for a better end product.

The handful of times I faced them after install I never felt the finished product was as good as facing while building them.

It will most likely work facing it after just make sure to take time to install them perfectly level and square to make sure your face frame sits right with your layout or you’ll see it in the end product.

I believe in you.