This indicates it was put in service during the war. It doesn't say that specifically about the 4C but it looks like it. Any chance you're wrong about it being post war? Flying either the 1C or the -4 is a blast, I can only imagine a 4C.http://www.voughtaircraft.com/heritage/products/html/f4u-4.html
Maybe 924 rounds per side.
IIRC, the F4U-4C didn't have the Hispano, it had it's own American made 20mm gun.