Yeah the connections on the right are indeed pretty obvious (or at least documented), what was less obvious is that PWM is also available on the 6-pin ICSP header on left side of the board, and it made a big difference for me as I was able to plug a female dupont cable onto these pins and get that signal with no soldering required, i.e. without the need to unmount the controller board.
By the way, just to document what has been said above for future readers, the ISP header (on v2.4d and probably all boards going back to the dark ages) has this pinout:
pin 1 = D12 = MISO = LIMIT Z
pin 2 = 5V
pin 3 = D13 = SCK = SPINDLE DIR
pin 4 = D11 = MOSI = SPINDLE PWM
pin 5 = RESET
pin 6 = GND
and the pins are arranged like this when looking at the board with the USB/power connector on the left side:
2 | 4 | 6
1 | 3 | 5