I'd definately go buy an s13 and drop an rb26 in it..
Even a standard sr20det s13 with exhaust, fmic, upgraded turbo, boost, suspension, computer.. will absolutely haul ass and be a hoot to take to the track.
Because this is a skyline site, you could go the r32 gts-t with rb20det and the same mods.. your going to get better times with the same mods and less money spent in the s13 though. Just make sure you get a whiteline kit so it takes the corners more like a race car and less like a drift car.
Your going to need some pretty wide tread on it as well..
Do you have a budget in mind? Maintenance? Rebuilding an rb26 will cost more than an sr20/rb20