I see a return spring on your engine hook danny, and then on Loyds car no return spring there, but both of your cars have the water neck with a provision for the return spring, I am pretty sure my water neck doesn't have the provision for the spring. Did all 69 Z have that provision? or was this insignificant enough where some had it and some didn't?
Or just early cars had it? (didn't mean to hijack just curious if this has been raised before or noticed)
All 660 thermostat housings had the provision for a return spring, but it wasn't used - the spring was anchored at the REAR, on the spark plug wire support; bad design that accelerated wear of the primary throttle shaft holes in the baseplate, but that's the way it was.