ORIGINAL: Woketman
I do not think that you need to worry about adding a magnet in the nut on an old manual air start AMT. IIRC, they have no magnet. The RPM sensor detects the compressor blades passing by it. No magnet is involved. At least that's the way I remember it.
Thats correct.
BTW - my friend's AMT Mercury has been modified with a JJ1400 starter and its working great.