Single ground is OK as you suspected.
The warming resistor is actually still there (330 ohm, 7W - the physically smaller one is warming).
The voltage dropping resistor is missing. You need a 5 ohm, 10W resistor put back in the open spot.
Part number RC10W-5 at GPE www.greatplainselectronics.com
If you want to stock up on the warming resistors, they are part RC7W-330