In response to your question: The pairs of tubes in a VT-100 sit next to each other.
I am not sure of the "V" numbers, but the easy way to remember is:
When you look at the amp from the faceplate,
Left front 2 output (larger, on the top) tubes are a pair; Left rear output tubes are a pair; Right front 2 output tubes are a pair; Right rear 2 output tubes are a pair. You need to get at minimum matched pairs of 6550s, matched quads or Octets of tubes are even better.
When you bias them, the test points are the big grey resistor between the 2 pair on each side. The bias (value written on the circuit card). Be careful -- there is 460V running on the traces of the amp, and let the amp warm up for at least an hour before adjusting. Make sure the input is muted when doing the adjustment.
Some of the advise is good above, make sure you turn both bias adjustments to 1/4 of the value with the existing 6550s installed before new tubes are inserted. Failure to do so will most likely blow a screen resistor.