Start with a late model 3.2V6 gives you 240hp / 213 lbft.
Upgrade the brakes
with braided hoses, red-dot drilled and grooved discs and Ferrodo DS2500 pads.
rear and maybe front too if you're fussy. Upgrade the suspension with 20-30mm drop
or Bilstein dampers.
Add the Q2 differential
to get the power down and improve exit speed from corners.
Then you can start to work on the power. BMC CDA
will add at least 8hp, possibly as much as 12hp. You could change the cams
too for another 12-18hp but the improvements are mainly at the bottom end and given the immense grunt of the 3.2 I'm not sure it is worthwhile. Upgrade the exhaust
with downpipes, sports cat and mid and rear sections to release another 12-15hp and save some weight.
That should bring you about 280hp before a rolling-road remap by red-dot or AHM gets you 290-300hp, though by then you may need bigger injectors to avoid running lean.
Wheels are fine with 17" but lighter weight OZ or BBS would be better.
Also you could lose some weight - there is easily 250kg you could lose from the interior and air-con. You can get lightweight panels too. You could improve power/weight ratio by 15%+ by stripping stuff out. With all these things power/weight ratio could go from 160bp/tonne to 230hp/tonne.
Most importantly don't drive it around like an idiot
Bearing in mind this car will be used to take on the ringroads every Friday and Saturday night and pushed to its limits. I did this with the Galant and the car couldn't even come close to keeping up with me.