The most useful fact is that Z10s were not pace cars and had no association with the 1969 Indy 500. The Z10 option was described on factory documentation as "Special Accent Striping." Z11 is described as "Indy 500 Pace Car Accents". I don't believe any dealer info has been found to explain the Z10 option. The US Camaro Club had a registry but is now in limbo. Maybe someone will know how to contact them.
The Z10 is a low production car. Often refered to as the pace car coupe. As stated above it shares white paint and orange stripes with the Z11 and may have been an RSSS (not sure) but had no ties to Indy.