I doubt if the ignition coil makes any difference. The CDI box can be had for a lot less than that. I think I paid about 30 bucks for mine back when I was diagnosing electrical problems on my 91 RM125.
I don't know how much of a difference the CDI mapping makes since porting, squish band, powervalve tension, and expansion chamber affect powerband as well, but if it makes it anything like my '91 RM125, with the 300's power, it would be downright scary. I had the 125 bored over to 144cc and once I dialed in the jetting it was unreal. I didn't know such a small bike could throw dirt and tear up tires like it did.