I'd say full-length subframes, long-tube headers, O/R X-pipe (or hi-flow cats if you have emissions testing), a Chicane pulley, 3.73 or 4.10 gears, some upper and lower control arms, and you'd still have change left.
All the mods listed above are excelent, and will make a nice overall improvement (except for one)
plus maybe a Chicane rip kit ( basically an air intake, filter setup) Or just custom fit up a bbk or mac cold air kit ( they will fit)
I would honestly stay away from 373's let alone 410's... Im sure your aware of how much wheel spin your getting now, with the 327's.. why would you want to amplify this with gears? you wouldnt..