Definately agree with burpin. Don't be a pest. The pesty fly always gets swatted. If he's a nice car guy type of guy, he may call you back and say sorry, not for sale, but you could still talk to him about the car. Flatter him, as previous posts stated, and tell him to put your number in the glovebox and if he ever decides to sell to give you a call. See if he goes to cruise nights and see if you can buddy along. Get him to remember you. You always hear these stories of guys who don't want to sell then turn around and do.
If he doesn't call back, if you really want that particular car, leave another note in a month or so. That's what I would do.
"you never know if he just got back from the local Walmart and the Dang thing ran hot again or he noticed a knock and has had enough"
I agree. The original owner of my Challenger sold it because he thought he "blew the engine" when it over heated. The neck of the radiator fell off, I soldered it back on, and it seems happy for now.
Notes don't hurt. If I need parts and I see a Mopar in the driveway I'll leave a polite note saying who I am, why I'm leaving a note, how I know this car is here, etc.. so the guy doesn't think I 'm some weirdo looking to steal his car or something.
Hope you get it. Let us know if he calls back! (I'm in your boat. I have a 4 year old son that's car crazy!)