I have a 16HP Briggs 'n' Stratton when she's ready to go fast! My brother built a couple of the small stroker Honda engines for his boss's kid. Some of those Jr. Dragsters are faster than "built" Hon... Oops, I mean certain cars
You can get the master links from any mower shop. With that type of engine thats were most of you're shopping is gonna be unless she really wants to get into it. Then you might wanna look up the Phantom series shifter karts. My oldest nephew races one and them lil basterds are fast! Dangerous, but uber fun!