I just got another Fox with the rounded detent lever. It SUCKS. Balls roll right over it, as it doesn't stick far enough into the chamber to reliably detain them, and there's not a lot you can do about it besides trying to open up the notch in the upper body where it rides to allow it to stick up farther. I was having lots of double-feeds last Sunday. I never had this problem on my other Fox with the squared-off detent.
Other differences I noticed are similar to yours. My older (silver, standard) Fox has the trigger plate slop you describe, while the new (black deluxe) Fox's is rigid. I noticed on my Alley Cat that I could fix the slop by tightening the bejeezus out of the pivot screw, but that didn't work on the Fox.