Looking into this further I've decided now to lengthen the magazine box in front of the shoulder ridges but to lengthen the mag cutout in the receiver in the rear by .130".
There just isn't enough room in front to allow a proper feed ramp without compromising the strength of the bottom locking lug abutment.
I'll have to shorten the ejector blade and thin the right side baffle lug to allow more rearward travel for the bolt.
Should be an easy milling job.