Job is done. I get full 40-meter coverage without birdie on 7.023 MHz because my digital VFO outputs operating frequency plus BFO frequency. The bandwidth of the crystal filter seems a bit wide and I will figure out later once I have time.
The sidetone is pure but a bit low. I will adjust the frequency delta later. The RF output is 1.2 watt. Not very good but acceptable because I replaced the PA transistor with a BD139, very cheap one.
I believe the modification of NC40A is very necessary to fix my issues. As an experiment, I am quite satisfied with what I have now.