You may want to make a gas RC electric as I show you for a few reasons. One methanol costs $30 per gallon after you drive to Hobbytown to get it. Two you don't like using fossil fuels for fun. Or three you have a gas RC with an engine that has low, compression like me. This can cost you about $40 on nitro rcx.com (not including shipping).
Step 1: take the engine off
First you will have to take the engine, speed controlling servo, battery case, and fuel tank off. If you stripped the head of the screw too much I suggest using a cutting blade on a dremel and grind through the center so you can make it a flat head.