Found this info, dunno how accurate it is, but it seems to me that there **Might** have been some cannon- 4's before the end of the war

F4U-4 1944 = Upgraded 2350hp R-2800-18W, new cowl design, four-bladed prop; armament: six .50 guns, eight wing rockets, two 1000# bombs; length: 33'8" load: 3215# v: 446/215/89 range: 1005 ceiling: 41,500'. Production also scheduled by Goodyear as FG-4, but contract was cancelled and none built.
F4U-4B 1945 = POP: 287 scheduled for RNAS as Corsair I, but cancelled with the end of hostilities.
F4U-4C 1945 = Four 20mm cannons. POP: 297.
F4U-4E 1946 = Night fighter with APS-4 radar. POP: possibly only 1.
F4U-4K 194? = Radio-controlled target. POP: 1.
F4U-4N 1946 = Wing-mounted APS-6 radar. Might have been an upgrade of -4E. POP: 1.
F4U-4P c.1946 = Photo-recon modifications; POP: 9.
Alos found this at :
Marine Corps Historical Reference Series249. F4U-4 Fighter, 1-engine, 1945 Vought Pratt & 33'8' 41'
1-crew, land/carrier, "Corsair" Whitney
inverted gull-wing R-2800-18W
monoplane 2200 to 2400 h.p.
250. F6F-5E Fighter, 1-engine, 1945 Grumman Pratt & 33'7" 42'10"
1-crew, land, "Hellcat" Whitney
low-wing monoplane R-2800-18W
2200 to 2400 h.p.
251. F7F-2N Fighter, 2-engine, 1945 Grumman 2 Pratt & 31'2" 51'6"
2-crew, land, "Tigercat" Whitney
high mid-wing R-2800-22W
monoplane 2200 to 2400 h.p.
I'll take the tigercat pls!

tank you!
Hamish!