Never heard of a neutral safety switch on a manual transmission. I imagine it would be a challenge because of so many positions the stick could be in. It would be easier to rig it where the clutch pedal must be depressed to start I would think.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.