Michael,
It sorta depends on which Nascar Polar Lights kit(s) you're looking at. In my opinion, the early-1970's Dodge Charger Nascar kit has a few, not-too-major racing chassis errors to it, but the Charger body is "way-off" in it's shape and accuracy in a lot of places. With some work, it can be built to look okay, but the body would take a lot of work to get it's shape correct, (I'm not sure I've ever seen one built-up that looks correct, even after major bodywork).
The 1969-1970 Ford Torino Talladega/Mercury Cyclone Nascar kits have a somewhat better chassis, and offer two engines in each kit, but these kits have two major problems. The first problem also involves the kit's body; the front fenders on the bodies are molded "flat" across their tops, making the nose of the finished race car sit-up way too high. (In the kits that I have, those front fenders almost appear to be molded "going uphill" from the wheel arch forward to the front bumper, which is nothing like the down-slope on the actual 1:1 race cars)!
The other problem is that both engines provided inside these kits are a bear to fit into the racing chassis! The 429 motor doesn't really fit the chassis correctly at all, and can lead to other building issues like hood fit, etc. The kit's 427 engine fits better, but it too, has some fit issues.
A couple of questions about this kit: Did this kit have separate pieces for it's rear suspension, (separate axle, leaf springs, shocks, etc.), or is the entire rear suspension molded directly into the main chassis piece? Does it use a steel-wire front axle that passes thru a hole in the engine block? Thanks!