One thing I'd keep in mind using NOS pistons from that era - I would have each one measured and then compared to each individual bore to determine if they will provide proper piston-to-wall clearance. Only then could an informed decision be made on usability.
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.
