My 1970 442 has the windshield washer bottle mounted on the driver's side and the coolant over flow tank mounted on the passenger side. I read that most dealer installed coolant overflow tanks were done in the this matter. Thoughts?

 

I didn’t know Oldsmobile was still using the washer bottle in 70, my 71 Cutlass has a plastic washer container that is mounted on the drivers side and the overflow on the passenger side.

 

The washer tank was mounted on the passenger side on all 1970 Olds A-body cars that came with the 455 and the larger battery. Your 70 should have come from the factory with the holes drilled in the passenger side inner fender to mount the washer tank there. The overflow tank didn't exist in 1970. Any retrofit of the later overflow tank conflicts with the washer tank. Moving the tank back to the driver's side requires reverting to a smaller battery.