I've got the Buggyra which I took the manget out of, added some weight and some Indy's. I run the stock tires on the inside. I did cut away a bit of the sidewall and superglued the tires together and then to the rims. I took the spring out of the guide and made it sit a bit lower in the front. It is a beast and a shedload of fun to drive. Of course there's all that mass approaching a corner.
Mark