So with the possibility of not finding any original paint being discovered after my further research I would not be out of line with painting the chassis a medium gray family with a little metallic thrown in for a June 12 69 car..
I would instead apply a dark gray with a slight blue or greenish tint which is more common. In 69 not allot of wild or bright colors as in 70 when the batch colors can take on a much wider range of colors from what I've seen. Firewall rearward - over bare metal
One issue I need clarification on. With batch paint am I understanding that there would be no red oxide as a base under the batch color for the under floor of the car nor under the strut rod channels or exterior shock towers or is fire wall forward still red oxide base?? Sorry guys. I am reading a lot of posts and the more I read the more I see twists and exceptions...
For a June built Dearborn car I normally see red oxide over bare metal covering the inner fender wells, frame (all three sides), into all the pockets (strut rod, lower a arm, bottom of sway bar mount...) and the inner surfaces of the shock towers. All this before any of the other colors get added to the surface
Don't worry or get distracted with the exceptions or oddities IMHO since you have no documentation of yours being different your better off served as going with the "norm" at this point.