73 340 with 051 heads

Agreed on the loss on the lower rpm scale.
Once you start moving, it's all good and not an issue. Power increases everywhere.
Absolutely nothing wrong with staying with the smaller valve. However since the head is old and may have had work prior, I voted for the 2.02's. But if the 1.88's are what he wants to stay with and its the engines first rebuild, no harm or foul.