The little William Green book says that the P-47C had the fuselage extended 8 inches at the firewall and a new engine mount employed.
Now, note that the fuselage was extended 8 inches, but the engine mount is bolted to that and we don;t know what effect the new engine mount had, if any
The P-47B was 35 ft 3.25 inches long and the P-47C-5-RE was 36 ft 1.75 in long, That is a difference of 10.5 inches, not just 8! So I can only assume the fuselage was extended 8 inches and that the new engine mount added another 2.5 inches.
Thanks for asking! I had wondered about that.
By the way, the P-47M and N had the later C series engine and were 36 ft 4 inches long.
Now, the next question is: Which P-47 model kits have the correct length?