I bought my P3 steel frame back in 2015.  It is the non XL version that supports a mk3 heat bed.  It was also the one that didn't support t8 lead screws directly.  There is a bearing holder out there that converts it and I've designed the LCD mount so as not to interfere with this mount.

You will need m3 bolts and nuts.  Attach the mount to the frame first and then attach the case back.  Screw in the screen with the supplied m2.5 bolts and then snap the screen cover over.

Note: the image of the printer z axis top is the right side.  The mount is designed for the left side, but you could mirror the mount if you want to use this side.  I took a picture of the opposite side so it was clear that this was the OG P3 steel.