To convert a C to an E would take quite a bit of work. Essentially, the entire nose section is longer and the radome is narrower, not to mention the addition of the gun. The E is pretty easy to find. Hasegawa makes one, Revell/Monogram released the Hasegawa kit under the Pro Modeler line, and I believe Testor's had one, but it wasn't up to the quality of the Hasegawa kit. I'd check Ebay to see if there are any available.