@FrAmiga
don't worry, you are refering to the same oscillator (the 3rd one). The 2nd one should be a 50Mhz one and the third one I guess that it will be a 66Mhz one.
@Puppy:
Ey tio! ;-)
"6:- 68K clock source, Oscillator 2 (default), oscillator 3 (alternative). System devices continue to be clocked from oscillator 2 when alternative is selected. "
You should change the 6th jumper located near the simm slots, near the edge of the board.
Be careful and check twice that you are changing the right capacitor.
I hope you assemble your A4000T soon so I can meet you at Euskal Party ;-)