Well, I'd be unhappy with 1. any unchecked movement of a rotary sort, and 2. with any discernible sloppiness in the end housing which allowed discernible up and down or side to side movement.
If the ring isn't central, and/or if it can turn 40 to 60 thou at will, you can kiss accurate timing goodbye.
If you can't really move it up and down or side to side in the housing, then it may be possible to locate it well enough by that third notch with the peg (or an oversize version) and eliminate the rotation problem. The thing is, if there's any fretting, it'll only get worse. I doubt you can rely on the end cap to hold things tight - and anyway, you can't tell what's what when it's on.
I didn't know there was such a thing as a universal cam ring, and I am having a rare cynical moment believing it might be a cheapskate pattern part rotten bad idea. If I had a spare fixed cam ring of the original sort I'd willingly give it to you.
If forced to use it . . . I'd either make a bigger locating peg to get rid of the rotational movement, or contrive an additional locating grub screw. I'd put the ring in and then check the points gap was close to the same on both cylinders (which it will only be if the ring is in the middle of the housing), and maybe use something like low strength loctite to help keep the thing where it's meant to be.
I dunno, I donta kinda like it, but maybe I'm being too picky and it will all be OK. Other better counsel may be at hand!