Someone has used this great little switch on their similar project with great success...

part # 62475K22 from McMaster Carr (what I was looking for the first time, NOT the mini switch)Hand-Operated Miniature Air Control Valve Spring Return, 3-Way, 1/8" NPT Fem Inlet, Push ButtonIn stock at $16.93 Each

I think I'll go this direction. I stopped at the fitting shop today to inquire about vaccuum tubing at fittings to connect to the valve switch. A couple easy compression fittings and it's all plumbed up. Push button... vac to fuel shut-off.