Interesting question! First the RS grill (and tailpan) on a 69 is slightly wider than a 68 (a couple inches). Also the fenders where the grill meets is a little more rounded than a 68.
But the fenders are metal and the grill is plastic. Both can be cut and welded/glued, so if you have skills (&money) anything is possible
My question would be: even though the 69 RS grill is flatter than a standard, would there be enough room for an aftermarket electric headlight door mech to mount to a 68 rad support and still have room and geometry to operate?