Yes! If I understand correctly you are planning on putting a magneto with a fixed cam ring and auto advance, in place of your manual A/R magneto. Of course you will lose the manual A/R facility. If you have to use the manual A/R when riding, maybe because the bike pinks under load, you will have lost the ability to overcome this. If you never use the manual A/R, other than for starting, you may not notice the difference.