If you can't do 12's with a big block then something is wrong. I ran high 11's with my 383, TH350 and a BW 9 bolt with 3.27 gears.
My new BBC "should" put me in the low 11's with somewhere around 550hp. The only reason I didn't build it to put me in the 10's is that I don't have a 9" diff yet and I expect to break my beefed up 10 bolt sometimes this year. One I get a 9" under the car I can always do a cam swap to get me in the 10's later.
As stated above, dropping in the BBC engine alone isn't a good idea. You'll need to work on chassis and suspension to handle all the extra power.
As for emmission, if the engine is built properly it should pass a smog test. Lots of BBC trucks still driving around that can pass. I drive my 454SS daily but don't have to get emmission tested.
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block almost ready for the 2001 racing season Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley