Thanks for posting your mods, I will review and learn some more.
No 0.1 uF sounds way to large to add to c81. If a rig has a severe dip at 40m, like only 2 or 3 watts, adding something like 100 to 300 pF will improve it. Try what you have, it will vary by rig and may not be that sensitive to exact value, just like the real difference between 5 of 6 watts to be barely discernible to the receiving operator.
For v4 harmonics, either substiting axicom relays or adding a separate set of relays on a daughter board should reduce them. Axicom relays appear to also reduce leakage resulting in mixer spurious, on some of our tested units. Others add shielded inductors at l5 and l7. Note harmonics impact bands 20m and below, and mixer spurs on 17m and above.
73 curt wb8yyy