Sorry I didn't get back to you sooner, been busy. Noise CAN be an issue, but need not be. Mount the ECU as close to the battery as you can, and wire directly to the battery. Del City has a really neat item to mount up to 4 wires directly to the battery, it can be seen here
http://www.delcity.net/delcity/servlet/catalog?parentid=789164&page=1 Also, shield any wires you think may give you trouble, like the tach lead. (A mic cable makes a good shielded cable. Ground only one end of the outer shield.)
I have a noise issue with my Corvair, but it is not the fault of the MS. I am running a GM 7 pin ignition, (no vac or centrifugal advance, all ECU). I am using the GM module, probably should have used the VR circuit in the MS but oh well. With an MSD blaster 2 can coil I never had a problem. I changed to a hotter coil, an epoxy unit recommended for the GM ignition, and then I started having the noise problem. It would cause misses, and timing jumps around 3500+ RPM under light load. Under heavy load, the noise did not become an issue until higher up if at all. I put in a digital Mallory box, (like the MSD). I thought that would help. It made no difference. I then twisted up the VR wires as far as I could without unwiring a bunch of stuff. That moved the noise up to 4000 or over, again under light load, heavy load is not a problem, or very little problem.
I broke a starter nose and have to pull the drive line anyway to dig out the bits of starter to protect the bell housing, so I am putting in a 3.89 gear, (replacing a 3.55), and will pull a lot of the wiring and redo it with all twisted pair wires. I think that will fix it.
I know this post does not have anything about the SOHC bike, I am only posting this here, rather than sending it privately, because I think this info is of use to anyone thinking of a MS for their SOHC bike.