I know you said you don't want to do this....but the cheapest option would be to spray it. 500 bucks or less if you get a used kit and you're done.
The big block option would not be even on my radar....unless you don't mind spending a little more, and don't mind doing a BB conversion (if you're good with that, then go for it). A stock big block in an A body is still going to be too slow more than likely. You would have to do some of the same things to the big block to get it in the ET zone you are looking for (cam, carb, intake, converter) + special mounts + BB trans + A body BB headers to get it in the car. I have seen more than a few guys that put big blocks in their cars expecting it to make some astronomical change, only to find out their car is not much faster...if any. One of the guys I race with swapped from a mild 360 to a mild 440, gained nothing (except a lot of weight on the nose of the car)...actually, I think it slowed down a tenth, but I'm not certain (runs 12.8's). My point is, no matter what you put in there (small block or big block), it will take some extra $$$ to make it in the 12's.
You will be handicapped by keeping those gears, but I would go the LA 360 route, home port the heads (lots of time, but very little money involved), put a decent size cam in, + Airgap + 750carb + a GOOD CONVERTER...this should do it (that's about $1500 if you shop around for parts and do all the work yourself).