I don't think $12k is going to buy you either of what you want. Unless you can find someone in a tight bind who is willing to give away their car.
Although right now you could get you a GN for under $12k or even a T type that might be less....doubt they're going to run 10's or 11's....you could make them run that fast, but then you say you also want it to be "reliable"....well as you know, there's no such thing as cheap, fast and reliable....you can only pick 2....it takes money to build a strong car.
Same applies to a 70 Camaro....which seem to bring about the same, if not a little more than a GN, depending on condition. You could go with a 383 stroker/TH350 and a 12 bolt but you still have to reinforce the car if you want to pull 11's....plus you might even have to spin that 383...that wears out the engine quicker.
Remember speed costs money, how fast you wanna go? I'd say get the one you want, then plan on spending a little more to make it live up to your expectations. Just my 2 cents.