I don't want Greyhound to counter 222 as hard as a Stuart would (Abilities + 80 damage). 60 (or even 50) Damage would place Greyhound on perfect ratio of Fuel to damage ratio for LV damage and would mean that it wouldn't sometimes get countered by a vehicle that costs half as much fuel and is a no-brainer counter. 50 Damage would mean that it would take 7 shots to kill a 222 and 8 to kill a Luches - making it extremely inefficient as a LV counter still.
I ran a load of tests on the Greyhound a while ago: with its .50 cal upgrade it beats the 222 and fights fair with the Luchs. Given its a Luchs itself, that seems about right to me.
The Greyhound without the .50 cal is utter trash, so just think of the unit as also costing the 70 odd MU you need, like Obers.