I don't think the 1.88 intake valve hurt those engines at all. Lot of people said they saw no increase in power going to the bigger valve on a stock port head.
The '71-'72 340s had the larger thermoquad carb and better intake then the earlier 340s.
The earlier 340s really only had about 9.5:1 compression from the factory. The lower compression of the '72-'73 340 does hurt performance and requires a piston change to correct.
Stock 340 pistons are heavy on all the years. Pay close attention to piston weight when shopping for replacement pistons. Lighter pistons allow engine to rev quicker and put less stress on rods, crank, and bearings.