77 Nova Tranny Conversion

I own a 1977 Chevrolet Nova Rally and it is equipped with the stock 305 V8 and automatic tranny. I would like to swap the engine for something with a bit more power and along with it, move on up to a manual transmission. Just tossing the idea around at this point. Has anyone done this? How difficult is it to do? Anybody know where to get the parts? Thanks for any and all input.
DJPII