The CV-300 was a marketing designation (ie not on the Type Certificate) used to differentiate Convair 240s that were fitted (or retrofitted) with the Double Wasp CB16/17
Must have been when it was fitted with the -17
Dave, the -16 is listed on the TCDS. Approved engines for the 240,
CA3, CA15, CA18, or R2800-83AM3, -83AM4A or -83AM9
(20:9 propeller reduction gearing); or CB3, CB16, R2800-83AM5, -52WM1 or -99W
(20:9 propeller reduction gearing). Note: R2800-97W is equivalent to R2800 CA-18
John Deakin, mentioned previously, also flies a C-131 (military Convair 340), and comments, " Fuel tracking is much more important in this airplane than some. There is no way to physically determine the amount of fuel in the wings. There are mechanical fuel quantity gauges on the bottoms of the wings (gallons), and AC electrical gauges in the cockpit (pounds). Only keeping track of "probable fuel used," and "fuel added," and some combination of fuel quantity indications, we can be reasonably sure of the fuel status." Lessons may be in that final sentence.
Swissair ditched a 240 in the English Channel off Folkstone en-route Geneva - London on June 19th, 1954 due fuel exhaustion. Accident attributed to negligence on the part of both pilots, who had forgotten to 'fill her up' in London.
Forgotten? Or fallen afoul of John Deakin's warning? Fuel exhaustion does seem to be prominent feature.