From a couple of different Italian documents
Most of the CR.42 models had 460L of fuel. At least one model had 560L of fuel. I have not found mention of any drop tank use.
_____________max
_____________fuel______range_________________________NOTE
CR.42_______460L______780 km with ~110L reserve_____350L main + 110L reserve tank
CR.42_______560L_____1015 km with ~110L reserve_____350L main + 100L long range +110L reserve tank
Both of the above ranges are for standard clean airframes - not the AS model - at 345 km/hr at 6,000 m, with a fuel usage of 112 kg/hr (~152L/hr).
NOTE: In the document the fuel usage is actually listed as 112 kg/hr for both aircraft instead of 152L/hr. The Italians seemed to use a weight of 0.74 kg/liter, or 6.17 lbs/USgal for their 87 grade fuel, so 112 kg/hr works out to 152L/hr.
The other documents use different speeds and/or altitudes (mostly 5,500 m), so it is difficult to exactly compare with the above, but they seem to be in the same ballpark. I do not know if 345 km/hr is the best Vcruise for range or not.