If you're looking for a car that's 95% strip, and mostly interested in running 11's, I'd focus on a good clean body and straight subframes. Dusk Blue is fairly rare...less than 5% of 69's, which equates to about 10,000 cars or by my calculations means about 2500 cars left today +/-. You say you want a non-Z, non-SS, 350, 12 bolt and a 350 TH. You just described an LM-1 car. There are a few out there, but they're pulling almost as much as SS-350's.
What I'd do if I were you, is get a six-banger car with a good clean body...with less than 5% rust. Drivetrain is irrelevant. You'd rather it didn't run, so it'd drop the asking price. If possible, make sure it has all the trim. Trim can add up in a hurry as I continue to learn the hard way. Get it painted the color of your choice with base and clear poly. Purchase a 12 bolt,..fit it with posi and gears of your choice (4.10's would be start for a high revvin' 350 that pulls 11's). I've seen 12 bolt housings in the $500 range. 350TH are readily available used...you could get one that runs well for $200 at most any boneyard. Have it built to your needs for another $500. Then pick you a crate 350 or shortblock and build it to about 400 or 500 ponies. Beef up your subrames so you don't twist the car in two, then blast off!!!
Estimate: 11.9 et for $11,900
Car....$3500 (may be better deals)
12 bolt (built)...$1000
Crate...$4000 (several in price range)
Paint...$1000 (not show car, but good)
Wheels and tires...$ 800
Other...$1000 (stuff like, brakes!)
Bad *** Camaro that runs 11.9 et...$11,900 (rough estimate).
Then come to Ausitn...pick up ol' Sleepy...pin his eyeballs to the headrest. Watch Sleepy smile! Good luck!