BBs don't belong in 12 second a bodys, not really even worth the hassle till maybe mid 9s. Simple jobs like spark plugs are not simple, you stuck with a 727 if you want an auto and they are heavy.

The Gen III hemi is awesome but sooooo expensive to get it in (motor mounts, headers, oil pan, EFI or carbs are both expensive and painfull when you count "good" intakes that will eat most of $1000, all the accessories evn from the JY are still expensive, aftemarket flex plate) if you buy a drop out with the harness and computer it is expensive and eats all the $4500 when you throw in mounts, pan, headers... and you might get 400 hp without breaking it open. It is the lightest option witch is good and you should get in the 12s.

A 408 is the easiest, cheapest most fun combo. Get a set of EQ heads from hughes under $1000 ready to run. Get a SCAT rotating assy with I beams and it drops in with no grinding needed. Get the roller reground at delta cams for under $100 the one I use most is 221@.050 110 LSA and pulls like crazy and will runs 12s easily in an a-body. Motor mounts, oil pans, headers... are a dime a dozen, plugs are easy to swap, you can run a 904 for more weight savings and eliminate the traction issues a front heavy BB has. If you can not run 12s with this and keep it under $4500 you are paying someone too much.