I had an '83 zephyr (basically the same thing as the car you bought) but i decided to get a mustang instead because the car was a straight 6 and i'd have to get a bunch of stuff to convert it to the 351 i had i mind. My opinion on what you should do:
mild (or wild) 460 with a C6 trans, 8.8" rear with 3.55 gears all with stock steel wheels widened and enlarged to 15x7 front and 15x8 or 9" in back (by a company like stockton wheel service) and with wire wheel covers, as well as dumps for exhaust before the axle and the stock tailpipe or the tiny straight 6 pipe sticking out the back as a decoy pipe (the L6 pipe turns and goes behind the left rear wheel, is small and very visable). Go for the total sleeper effect!
although a 347 with a balanced combo (for example the edelbrock performer RPM package, etc.) with a built C4 (with shift kit, manual valve body, trans brake and higher stall converter) and 3.73 gears would make that thing go like crazy as well as the previously mentioned sleeper items.
Good luck, I'm jealous, i'd like to do a sleeper car as well, but i can only have so many projects.
------------------
'84 Mustang 5.0 LX
My car