"I have a phong 1655 case that needs about a .25 of a mill cut inside under the movement screw ring, it seems it’s not machined correctly for my 1570 movement."
One fix might be to use a knife edge screw in place of a square edge screw.
Something else when using casing screws with skirts...if the movement and dial does not turn freely inside the case when lining the stem up with the case tube, it can scratch paint off the dial when turning it.
I never did mount a complete GMT movement in my Phong '1655' case but did put a 1570 in it with the correct date spacer and dial to see how it would fit and it was Ok except for two tight spots. I ground a tool bit to remove the burrs inside the groove but never did anything to it because it is close work with very little room for error. You need to remove the bezel/crystal or carefully clamp over the numbered bezel to mount the case in a four jaw chuck and center it...either that or put it in a 'self centering' three jaw chuck and see if it centers after a few tries. I decided to try running a small 1 inch OD cut-off wheel around inside the groove a few times by hand (not in a power tool) and see if it would remove the tight spots. This would probably be Ok for removing tight spots but would be slow going to widen the groove all the way around while keeping the cut-off wheel level in the groove.
I have an MBK '5513' with the same problem and I used case clamps and screws in it rather than cut the groove wider. I have seen a few pictures of a 5513 with case clamps and screws.
Here is a picture of a genuine 1655 with knife edge case screws and afaik many/most of them came that way. They are easy to spot because the knife edge skirt is wider than on screws with square edge skirts.
https://sansomwatches.com/product/rolex-explorer-2-orange-hand-1655-steve-mcqueen-vintage/