As far as RX battery packs, use a 5-cell flat pack (the battery space will not accept a hump/3x2 pack) with at least a 1200mAh capacity. If you are going to run digital servos in the car, go with a high capacity. If you go LiPo on the RX pack, make sure that you either use a 6v regulator or opt for the new servos and receivers that are now capable of accepting 7.4v outputs of LiPo packs.
As far as servos, use a digital servo for steering for sure with at least 120 oz torque and high speed. The car is quick and you want to make sure that A) you can turn the front wheels fast and B) when they are turned, they hold in place and don't "chatter". For you throttle/brake servo, you can go either digital or analog but if you choose the latter, use the best on available (high speed and at least 80 oz torque). If you go digital with both, definitely get the LiPo RX pack (digitals use more juice than analog).
As far as bodies, the industry concentrates on Lola bodies for the car. Back about 15 years ago, they use to make sedan bodies for the car and if you search really hard, you may find someone with one out there. Also, check some Euro or Australian sources as far as hobby shops/websites; there maybe someone still making them for the lads across the ponds.
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The only thing that is for sure is that nothing is for sure!!!
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There are 2 things in life that are infinite: the universe and stupidity.