used first, before drop tanks
Okay, so we have 237 gals of fuel before entering the combat. This is not very different than what the razorback P-47 will got after it used the 60+- of it's 305 gal internal tank for warm up and take off to a safe altitude so it can switch to belly drop tank (110 gal British type was probably the best what it gotten in Europe in Autumn of 1943).
Such P-47 was rated for 375 mile escort radius. I don't think that F4U will get more than 5% more, 400 mile radius is probably stretching it.
OTOH, the F4U with additional internal self-sealing fuel tanks (not hard to do, just wasn't done apart from token number of F2Gs) would've been a fine long range escort.
B-24 cruise was 180mph. Stick with the Bombers unti fighters are sighted. F4U has far better climb and acceleration than the P-47 at the
bomber altitudes
P-47 was using 100 gallons/hr, so the F4U would have better range than that, but not as much as the P-51. Few things did
Fighters were required by USAAF to cruise at 310 mph (more precise, 210 mph indicated at 25000 ft) when escorting, so the LW has hard time trying to bounce them. Facsimiles of two tables describing the escort requirements are in the closing pages of the 'America's hundred thousands' book.
In order not to run from the bombers, fighters weaved above and in front of the bombers after rendezvous, so even book radius figures were true just for instances where relaying was used.
F4U might as well have better climb and acceleration than P-47 under 20000 ft, but above 25000 ft it was not so. P-47 was faster there by 20+ mph, the performance margin above Fw 190s being such that LW pilots were returning back after spotting the Jugs.