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.
No offense but you should be able to run 12's with nothing more than a 5.9 with a good cam, intake and headers with a set of 3.91's or 4.10's out back.
I'm running 13.0 with a 5.9 and 3.55's in the worlds fattest'74 Duster at 3675 lbs with driver while bucking a headwind at Lebanon Valley.
