Here's a link to an old thread here that may help:
viewtopic.php?f=21&t=1674&hilit=According to this the stator and rotor will bolt right in, with the coil and CDI box requiring some work to mount to the frame (I did this on my MR, it wasn't too hard).
I've bought a number of complete ignitions off eBay, and paid from $68 to $120 each including shipping. I was very patient and waited for the best price, though; if you need yours right away, expect to pay more. Any '74 to '78 CR125M ignition should work
providing the stator and rotor numbers match (examples are 4B 360B, 6A 400, 7H 400, etc.) I have a 5K 400 stator/rotor set I could part with; the rotor has just been remagnetized, but the stator has some rust on it (many of them do).
With a CR125M ignition (set at 2.2mm BTDC), pipe, and carb on a stock MT125 cylinder, your MT should perform a lot like a CR125M up to maybe 6,000 rpm or so, and will continue to pull much harder than a stock MT above that.
Try searching this site, I wouldn't be surprised if there's even more info available.
Ray