A3 Router Build

[JAZZCNC]

Jim the main thing I see with this design I dont like is the position of the Y Axis ballscrew. Because of the profile (looks like 90mm) It's too far back.
I would think about using either two pieces 90x45 (Or cheaper still 80x40 box) laid flat one above other with a gap between so the screw can go between and fasten directly onto Z axis backplate.

Or if like me you prefer the Ballscrew out the way round the back then use 90x45 (Or 80x40 box) arranged in an L shape and bolted together.
The slight difference of 45(40)mm doesn't have a big effect and I've built a few machines using this approach and it works ok with no visual difference in performance to when connected directly to back plate.
Doing it this way means you eliminate the back plate on Y axis and if you use 90x45 the Bk/BF12 blocks fit the slots and can be bolted to extrusion then the motor can bolt directly onto the gantry side or be inverted round the back if you want to belt drive.
This way use's a small drop plate to connect to Y nut but because like in your case your using the FK blocks then you could mount them higher and mount directly to the under side of the top bearing plate.

See Cad I did recently did to show some one and also pic of an actualy small machine done the same way, thou it doesn't show the drop down bracket.