That is an awesome mod. Some companies sell bodyshells. You need to reinforce the chassis as you typically take out the roof. Fit a roll cage for added rigidity and safety and for the ultimate engine go for a Porsche power plant in the back. Next you add the oversize wheels and hey presto you are there. It is a hell of a lot of work though. Do some searches on BAJA conversions for a little more guidence and welcome to the site. Nice to have another crazy car modder on board.