70 nova 350 turbo-350 pushing 300 hp.

I've decided to replace my motor...it only has about 400 miles on it..but i want to get to a mid-12 1/4 mile time which seems to require alot of power when in front of a 3-speed. i have full capability of rebuilding a motor and throwing a 700r4 behind a built small block or this carbureted LS2.

http://www.jegs.com/webapp/wcs/store...tegoryId=10763

now...my question is...price wise and an eye on MPG whats the best way to go? the LS2 or a small block i build up?...to get mid 12"s?

the 2nd question... i have a turbo 350 auto on the column. i really want a TCI manual/automatic valve body transmission on the floor so i can race on the strip and control shift points or cruise around town in auto. is it difficult to retro fit? what all is involved? what transmissions should i look at? keep in mind i want at least a 4 speed.
Thanks for your time...