If you're using the Ramesses II, then you do not need to do any modifications to the motherboard. Installing the Agnus adapter and the Gary board is enough.
You'll notice the Ramesses manual has info about the Vbb jumper, which you must set to match your Agnus. The rev 6.4 capacitor modification was for the same reason - they shipped with a Vbb Agnus, so the capacitor was needed. The Ramesses II does it for you, so all is good.