Join Date: Sep 2000
Location: Washington, Michigan USA
Vacuum advance (with manifold vacuum, not "ported" vacuum) will let it idle smoother, run cooler at idle, improve off-idle transition, and improve fuel economy. Unless someone butchered the distributor, a replacement advance diaphragm should bolt right in (you have to pull the distributor and disassemble it to install the advance unit, as it goes underneath the breaker plate).
'69 Z28 Fathom Green