As mentioned above, the SCCA Improved Touring rules require stock engine internals, cam, valvetrain, etc. There is no value in doing IT specific tuning to an engine that is not limited by the IT ruleset. Its A LOT of work for a minor gain in horsepower. You can get all of that and a lot more with the aftermarket cam mentioned by Tony above and by installing a Megasquirt EMS.
All that being said, the best SCCA Improved Touring L24 engine I know of made 208hp on a SAE certified/correct engine dyno. That engine won the ARRC two years in a row. To have that engine built today expect to pay about $8,000. You can have an engine built using aftermarket parts that matches it in horsepower for about $3,500.
FYI... The 280Z is not, and never was, competitive in ITS due to the weight required and you can pull more horsepower out of an IT spec L24 then an IT spec L28 because of the rpm you can spin the L24.
Also, the tricks mention in the first post are correct and IT legal except the timing was generally run at 36 degrees all in by 3,200 rpm with a straight line advance (no curve). Vacuum advance blocked off and advance plate welded.