I've built the WSPR-TX_LP1. I used an arduino nano, a Si5351 module, a NEO-6M GPS module and a 74HC244 instead of 74AC244.
Output power of Si5351 module is 40.7 mW @14 MHz.
Output power of 74HC244 is 123 mW @14 MHz (without filter)
I used T37-7 toroids for LP filter.
Anyway, I prepared an UNUN with a 1:2, 1:3 and 1:4 turns ratio. Under all conditions the output power is 70 mW.
They are the results of my experiments.