look at the casting date on the block..if it was cast in 72, the engine would actually be a 73 model...
yes..you can change out pistons...but the engine will need to be rebalanced.
as the earlier pistons are heavier then the later low compression pistons,,,,,
or use KB243 pistons which seem to be lighter
Will these kb243 pistons put out the 10.1 compression as the 71 340?