Steve, other than the bodywork, the seats have to be in a more upright position (likely the way your Margay already is). Double rear bumper, which extends out to at least the mid point of the rear tires. They are generally a bit wider. Usually 50″ minimum and 55 1/8″ max. across the outside of the rear tires (although 4 cycle sprint racing allows them to be much narrower). Many rules set require specific size and/or size and brand tires. For instance WKA requires 4.50 x 5 fronts; 7.10 x 5 rears, Bridgestone “C’s”.
May I strongly suggest, before you spend a bunch of time and money on your older kart, go to a track or two and have a look. There are many older karts out there that can be had at a very reasonable price. That may be a better deal then upgrading yours. Check the classified ads on this site, and there is a LO206 Facebook page as well.
I noticed you live near Fredricksburg, Va. If that’s the case, the Woodbridge Kart Club is holding a road race event at Summit Point on Apr. 29th and 30th in Summit Point W.Va. We’ll be on the Shenandoah circuit if you’re interested. There will be a lot of CIK chassis there for you to look over. In fact we will have two WKA legal CIK chassis’ with LO206’s on them. You are more then welcome to stop by and look them over and ask any questions you may have. If you do decide to stop by, please look us up. Most folks at this event will know where the Gaynor’s are pitted.